Objective To investigate effects of FK506 on function and revascularization of transplanted islets after pancreatic islet transplantation (PIT) in diabetic mice. Methods Pancreatic islets of donor mice were obtained by infusion of collagenase P solution with pancreatic duct and Ficoll-400 density gradient centrifugation, then transplanted into renal capsule of type 1 diabetic mice. The recipients were divided into two groups: control group (PIT group) and FK506-treated group (PIT+FK506 group). The blood glucose of recipients mice after islet transplantation were monitored. The histological feature, function of insulin secretion, and revascularization of the grafts were observed. Results The blood glucose on each time point had no significant differences between PIT group and PIT+FK506 group (P>0.05). Histological examination showed that all the islet grafts survived well and had no difference. On day 3-5 and 20 after PIT, compared to PIT group, VEGF and CD34 expressions were significantly lower in PIT+FK506 group. On day 3-5 and 20 after PIT, the newly-formed microvascular density of renal subcapsular islet grafts post transplantation in PIT+FK506 group (9.3±1.0 and 61.0±2.7) were significantly lower than those in PIT group (16.6±1.3 and 96.7±2.3)(P<0.05). Conclusion The therapeutic dose of FK506 inhibits the revascularization of transplanted pancreatic islets, but does not affect the insulin secretion of the transplanted grafts directly.