Purpose To quantitatively examine changes in macular oedema after phacoemulsification surgery in eyes with diabetic retinopathy (DR) and in eyes without DR. Methods Thirty-four eyes with DR and 34 eyes with no DR scheduled for phacoemulsification surgery were recruited. Foveal thickness and macular volume were measured using optical coherence tomography preoperatively and at 3, 6, and 12 months postoperatively. Grade of diabetic macular oedema was also examined. Results Preoperatively, there were no significant differences between groups in foveal thickness and macular volume. The foveal thickness increased by 20.3% in the DR group and by 6.0% in the no DR group at 3 months after surgery, but thereafter decreased gradually. When comparing the groups, the foveal thickness and macular volume were significantly greater in the DR group than in the no DR group at 3 months postoperatively. The grade of macular oedema worsened in eight eyes (23.5%) in the DR group, and in one (2.9%) in the no DR group: the incidence was significantly greater in the DR group (P ¼ 0.0272). However, the oedema that occurred after surgery resolved spontaneously in three (33.3%) of the nine eyes. Conclusions The degree of diabetic macular oedema increases up to 3 months after cataract surgery, but thereafter decreases gradually. Grade of diabetic macular oedema also worsens up to 3 months, but certain percent of macular oedema that occurs after surgery resolves spontaneously. These changes are more prominent in eyes with DR than in eyes with no DR.