The antimicrobial, anticancer, and antioxidant activities of four cobalt (III) complexes, [CoL2]X (X = ClO4¯ (1); OAc¯ (2), Cl¯ (3), or NO3¯ (4) with hydralazine Schiff base derivative (HL), were presented. The structure of the newly synthesized complexes 1 and 2 was confirmed utilizing FTIR, UV-Vis, and NMR (1H and 13C) spectroscopy. In addition, single crystal X-ray diffraction was used to approve the structure of complex 1. Based on Hirshfeld analysis, the molecular packing of 1 is controlled by short HH, OH, NH, and HC(π) interactions. The results of the X-ray photoelectron spectroscopy (XPS) for the Co (III) complexes revealed the characteristic peaks of Co2p3/2 and Co2p1/2 with binding energy differences of 14.85–14.96 which greatly approved that the Co (III) complexes have been assembled successfully. Complex 4 (IC50 = 14.97 ± 0.59 μg/ml) has the highest cytotoxicity against lung carcinoma A-549 cell line compared to the rest of the Co (III) complexes and the free ligand as well. Also, complex 4 has the best antioxidant activity with IC50 of 283.4 ± 12.3 μg/ml. The free ligand has broad spectrum of antibacterial and antifungal actions, while the studied Co (III) complexes have good antibacterial activity especially the chloride complex 3.