Aims/Introduction: Epidemiological evidence for the effect of omega-3 fatty acids on the risk of type 2 diabetes is controversial. A meta-analysis based on prospective cohorts was carried out to evaluate this issue. Materials and Methods: Pooled diabetic risk was calculated using a fixed or random effects model. The dose-response relationship was assessed by meta-regression analysis. Results: The study showed that consumption of single omega-3 was associated with an increased risk of type 2 diabetes (relative risk [RR] = 1.45, P < 0.001); whereas the RR for mixed omega-3 was statistically insignificant. The dose-response curve presented an inverted U-shape of diabetes risk corresponding to the dose of omega-3 consumption. Subanalysis showed that omega-3 was inversely associated with type 2 diabetes risk in Asians (RR = 0.82, P < 0.001); whereas the risk was increased in Westerners (RR = 1.30, P < 0.001). Studies with follow-up duration = 16 years and baseline age = 54 years showed a positive association between type 2 diabetes risk and omega-3 intake. Conclusions: The present findings suggest that dosage and composition of omega-3, ethnicity, trial duration, and age could influence the effect of omega-3 on type 2 diabetes progression.