Purpose To evaluate the choroidal thickness changes after cataract surgery in type 2 diabetic patients. Methods Three groups of patients were enrolled into this prospective study. Group A included diabetic patients without diabetic retinopathy (DR) or with mild non-proliferative diabetic retinopathy (NPDR) who underwent phacoemulsification, Group B included non-diabetic patients with significant cataract who underwent phacoemulsification, and Group C included diabetic patients without DR or with mild NPDR who followed up without surgical procedure. Choroidal thickness in 5 points (subfoveal and 500 μ temporal, nasal, superior and inferior to the fovea) and central macular thickness were measured before surgery using enhanced depth spectral domain optical coherence tomography. Patients were re-evaluated 1 week, 1 month, and 3 months after operation and compared with the baseline values. Results In total, 63 eyes from 63 patients were enrolled to this study, including 21 eyes in Group A, 22 eyes in Group B, and 20 eyes in Group C. After three months of follow-up of the patients, choroidal thickness in all measured points was decreased significantly, and central macular thickness was increased significantly following cataract surgery in diabetic eyes (Ggroup A); meanwhile, both choroidal thickness and central macular thickness were increased significantly in non-diabetic eyes (Group B). In Group C, choroidal thickness and central macular thickness had no significant changes, after three months. Conclusion Unlike in non-diabetic eyes, choroidal thickness in diabetic patients decreased following cataract surgery.