AIM: To compare the changes in excyclotorsion after inferior oblique (IO) recession in patients with primary and secondary inferior oblique overaction (IOOA). METHODS: We retrospectively analyzed the data obtained from patients with IOOA who underwent graded IO recession. The patients were followed up for at least 3mo after surgery. Fundus photographs were taken pre- and postoperatively, and the sum of the angles of torsion in both eyes was used to analyze changes in excyclotorsion. Patients were divided into two groups: those diagnosed with primary IOOA were enrolled in the 1’IOOA group, and those diagnosed with secondary IOOA caused by superior oblique palsy (SOP) were enrolled in the 2’IOOA group. Excyclotorsion before and after surgery were compared between the two groups. RESULTS: A total of 78 patients were enrolled in this study: 34 eyes in the 1’IOOA group and 44 eyes in the 2’IOOA group. In the 78 patients, torsional angle significantly decreased from 15.31°±7.40° to 12.11°±6.53° after IO recession (P<0.001). Mean preoperative torsional angle was larger in the 2’IOOA group than in the 1’IOOA group (P=0.03). In both groups, excyclotorsion significantly decreased after IO recession (P=0.001 and P<0.001, respectively); however, there was no significant difference in the amounts of changes in excyclotorsion between the two groups. CONCLUSION: Excyclotorsion is significantly larger in secondary IOOA than in primary IOOA, and a significant decrease in the torsional angle occurs after IO recession in both types of IOOA.