Nowadays, various hazardous small molecules (i.e., antibiotics, insecticides, environmental pollutants, pesticide residues, and hormones) have become significant factors threatening environmental health. Tetracycline (TC), a common hazardous small molecule, has been widely used as a feed additive in agriculture and livestock breeding on account of its economic advantage, broad-spectrum activity against bacteria, and favorable oral absorption [1,2]. However, the abuse of TC can cause residues in food-producing animals and environmental media, and the consumption of such food or exposure to contaminated soil/water can cause serious harm to the human body, such as allergic reactions, skeletal dysplasia, and hepatotoxicity [3,4]. Additionally, it can cause the spread of super bacteria with drug resistance and reduce the efficient treatment of bacterial infections [5]. Therefore, the development of efficient platforms for monitoring tetracycline or other hazardous small molecules is an objective and realistic demand. Currently, the main methods of TC detection are chromatographic detection, bioassay, and immunoassay, e.g., high-performance liquid chromatography (HPLC), fluorescence assay, lateral flow assay, and mass spectrometry [6,7,8,9,10]. Although these traditional techniques are able to detect TC, there are shortcomings, including high testing costs, complicated operations, long detection time, poor reproducibility, and so on. Thus, an efficient strategy for highly reliable TC detection is critical. Indeed, various sensors have been rising to the challenge in becoming a feasible technique to detect TC, on account of their simple operation, high selectivity, and low costs, such as biomimetic electrochemical sensor [11], electrochemical sensor [12], electrochemical immunosensor [13], fluorescent sensor [14], etc. Alternatively, the photoelectrochemical (PEC) aptasensor has been drawing broad attention, owing to its low background noise, great sensitivity, and fast response [15,16]. It is worth noting that the PEC aptasensor can also directly realize the expression of the response signal without extra signal indicators, which is so practical compared to other sensors [17,18,19]. In PEC construction, the selection of appropriate photoactive materials is favorable to obtain a high efficiency and stable signal output [20]. Many photoactive materials (e.g., inorganic semiconductors and organic materials) have been developed to construct the PEC aptasensor, due to their unique PEC properties [21]. Among them, graphitic carbon nitride (g-C3N4) has been widely explored owing to its feasible photoactivity, low cost, and appropriate bandgap [22]. Nevertheless, pure g-C3N4 shows poor PEC properties due to its quick recombination of photogenerated electrons/holes, which restricts the construction of a high-performance PEC aptasensor [23]. Therefore, it is vital to effectively address this issue. In fact, a number of methods, including element doping, morphological control, and heterojunction system have been reported [24,25]. Inspiringly, the g-C3N4-based heterojunctions as an uncomplicated method are able to significantly improve the PEC performance of g-C3N4 [26]. For instance, a proposed PEC sensor based on ZnIn2S4/g-C3N4 heterojunction was developed for the sensitive detection of bisphenol A [27]. BiVO4 as a magnetic metal oxide possesses considerable merits, i.e., high visible light response, low cost, and low toxicity [28]. Researchers have pointed out that BiVO4 was suitable for decorating g-C3N4 owing to their well-matched energy-level structure, and the designed heterojunction has promoted the fast transfer of electrons and exhibited attractive and stable photocurrent signal [29]. Thence, BiVO4/g-C3N4 heterojunction could be expected to improve an increased PEC performance and be applied to the design of a PEC aptasensor for detecting TC.Herein, we fabricated a reliable PEC aptasensor based on g-C3N4/BiVO4 as an electrode material for TC determination. Additionally, the TC aptamer probes could be tightly assembled on the surface of g-C3N4/BiVO4 via covalent bonding interaction, to prevent it from falling off the electrode and further obtain a more stable and reliable signal response. When there is presence of TC, the aptamer probes could specially capture the TC and be oxidated by the accumulated holes on the photoactive materials and impede the electron–hole recombination, causing an enhanced photocurrent signal [30]. This work provided a promising method for a feasible analysis platform with excellent stability, selectivity, and detectability.