Post-stroke trunk rehabilitation often necessitates additional equipment or clinical assistance, which poses challenges in resource-limited settings. Although stable-sitting trunk exercises offer cost-effective alternatives, studies on their immediate effects are limited. Hence, this study aimed to investigate the immediate effects of five common stable-sitting trunk exercises on erector spinae (ES) muscle and postural control of stroke patients. A cross-sectional observational experimental design was employed in this study. The 11 paretic stroke patients recruited were asked to perform five stable-sitting core exercises on a customised force plate. The muscle activities of the individuals were measured with electromyography (EMG). Postural control measures such as vertical ground reaction force (GRF), and centre of pressure (CoP) were evaluated utilising the force plate. The ANOVA results demonstrated that the trunk rotation exercise (43.25 + 19.57%RVC) elicited significantly higher muscle activity in the left ES muscle than flexion-extension (25.47 + 17.70%RVC; p = 0.011) and sagittal-inclination (25.93 + 18.19%RVC; p = 0.017). Similarly, the trunk rotation exercise activated more muscle activity in the right ES muscle than in the other exercises. This finding suggests the potential of trunk rotation exercise as an effective addition to rehabilitation programs, especially in resource-limited settings or home-based interventions.