OBJECTIVE Stress urinary incontinence (SUI) primarily results from the weakness of pelvic floor muscles, working synergistically with the abdominal muscles. The current study aimed to compare thickness and contractile function of lateral abdominal muscles in women with and without SUI. METHODS Thirty-nine women with SUI (SUI group; age: 38.87 ± 8.96 years, body mass index (BMI): 24.03 (5.94) kg/m2) and 42 healthy women (control group; age: 36.21 ± 11.46 years, BMI: 23.90 (5.85) kg/m2) were included. Transverse abdominis (TrA) and internal oblique (IO) muscle thickness at rest and during abdominal drawing-in maneuver (ADIM) were measured with ultrasound imaging in B-mode using a Logiq S7/Expert device and a 9-11 MHz linear transducer. Percentage change in thickness and contractile function of these muscles were also calculated. RESULTS No significant differences in the thickness of TrA and IO muscles at rest and during ADIM between the groups were found (p > 0.05). The percent change in thickness and contractile function of both right and left side TrA muscles and the right side IO muscle were lower in SUI group than control group (p < 0.05). The percentage change in thickness and the contractile function of the left side IO muscle did not change (p > 0.05). CONCLUSIONS Women with SUI had a smaller percentage change in thickness and contractile function of TrA and IO muscle than women without SUI. However, there was no difference in the morphological features of these muscles between the groups. Considering the lateral abdominal muscle, training may be important for management of SUI.