This study is aimed to investigate the effects of subtenon injection of triamcinolone acetonide (TA) on expression of inflammatory mediators and retinal thickness in diabetic rats after laser panretinal photocoagulation (PRP) treatment. Diabetes was induced in male Brown-Norway rats that were subjected to PRP treatment with or without TA injection and sacrificed on day 1, 3 and 7 post PRR. Untreated healthy rats were used as controls. The diabetic rats showed significantly increased retinal thickness compared with those healthy controls as measured by optical coherence tomography. The retinal thickness in diabetic rats on day 3 post PRP was higher than in those controls without PRP treatment. And a significant reduction of retinal thickness in diabetic rats with TA injection was observed 7 days after PRR. Expression of vascular endothelial growth factor (VEGF), IL-6 and tumor necrosis factor alpha (TNF-alpha) was upregulated in diabetic rats and PRP treatment did not have a significant impact on expression of these genes. However, subtenon injection of TA reduced expression of VEGF, IL-6 and TNF-alpha regardless of PRP treatment. The results suggest that TA injection effectively reduce the retinal thickness caused by diabetes and PRP, and inhibite the expression of inflammatory mediators in diabetic rats with or without PRP treatment.