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<b>AIM:</b> To determine the difference of surgical induced astigmatism between conventional 20-gauge sutured vitrectomy and 23-gauge transconjunctival sutureless vitrectomy, and the influence of corneal pachymetry and intraocular pressure (IOP) on surgical induced astigmatism in diabetic patients.<b>METHODS:</b>This retrospective, consecutive case series consisted of 40 eyes of 38 diabetic subjects who underwent either 20-gauge or 23-gauge vitrectomy. The corneal curvature and thickness were measured with Scheimpflug imaging before surgery and 1wk; 1, 3mo after surgery. We compared the surgical induced astigmatism (SIA) on the true net power in 23-gauge group with that in 20-gauge group. We determined the correlation between corneal thickness change ratio, IOP and SIA measured by Pentacam.<b>RESULTS:</b> The mean SIAs were 1.082±0.085 D (mean±SEM), 0.689±0.070 D and 0.459±0.063 D at postoperative 1wk; 1, 3mo respectively in diabetic subjects. The vitrectomy induced astigmatisms were declined significantly with time (<i>F</i>2,36=33.629,<i> P</i>=0.000) postoperatively. The 23-gauge surgery group induced significantly less astigmatism than 20-gauge surgery group (<i>F</i>1,37=11.046, <i>P</i>=0.020). Corneal thickness in diabetes elevated after surgery (<i>F</i>3,78=10.532, <i>P</i>=0.000). The linear regression analysis at postoperatively 1wk went as:SIA=-4.519+4.931 change ratio (Port3) +0.026 IOP (R²=0.46,<i> P</i>=0.000), whereas the rate of corneal thickness change and IOP showed no correlation with the change of astigmatism at postoperatively 1 and 3mo.<b>CONCLUSION:</b> There are significant serial changes in both 20-gauge and 23-gauge group in diabetic subjects. 23-gauge induce less astigmatism than 20-gauge and become stable more rapidly than 20-gauge. The elevation of corneal thickness and IOP was associated with increased astigmatim at the early postoperative stage both in 23-gauge and 20-gauge surgery group.