[Purpose] This study investigated the effect of trunk stabilization exercises on the thickness of deep abdominal muscles and balance in chronic stroke patients. [Subjects] Twelve patients with chronic stroke were divided into 2 groups, an experimental group (EG) of 6 people and a control group (CG) of 6 people. [Methods] The 2 groups received routine physical therapy for 30?min, 5 times a week for 5 weeks. In addition, EG performed trunk stabilization exercises with visual feedback, using ultrasonic imaging, for 30?min. For the thickness of the deep abdominal muscles, the muscle thickness gap was measured with ultrasonic imaging. The Postural Assessment Scale for Stroke Patients (PASS) and Functional Reach Test (FRT) were also performed to assess balance ability. Muscles thickness gap, PASS, and FRT were measured before and after the intervention. [Results] Significant differences between the pre- and post-intervention values were observed for all variables in EG. A post-intervention comparison of the 2 groups revealed significant differences in all variables. The improvement rate for all variables was significantly higher in EG than in CG. [Conclusion] According to our results, trunk stabilization exercises showed effects in chronic stroke patients on both the deep abdominal muscle thickness and balance. The results support the idea that simultaneous application of routine physical therapy and trunk stabilization exercises can promote the recovery of chronic stroke patients and be helpful in rehabilitating them and improving their functional outcome.