Apoptosis is an important mechanism of immune-mediated graft damage. Nitric oxide (NO) generated by inducible NO synthase (iNOS) has been demonstrated to induce apoptosis. This study investigated whether apoptosis occurs during pancreas allograft rejection and examined the relationship of apoptosis of acinar cells and NO. The rats were divided into three groups: untreated isograft group, untreated allograft group and aminoguanidine (AG)-treated group. The pancreatic grafts were harvested on the post-transplantation day 3, 5 and 7 and were used to detect the histopathological rejection grade, the expression of iNOS and the apoptotic index (AI) of the graft. iNOS presented faint positive in the acinar cells of untreated isografts and did not change greatly after transplantation (P>0.05), the level of iNOS in the untreated allografts increased progressively (P<0.01) and at the same time point was significantly higher than that of untreated isograft group and AG-treated group (P<0.01). The transferase-mediated dUTP nick end labeling showed that the apoptotic cells were mainly acinar cells. A significant correlation between AI and iNOS was noted (P<0.01, r=0.611). Therefore, NO-mediated apoptosis of acinar cells plays an important role in acute rejection of pancreas transplantation, AG can mitigate the damage of pancreas allografts.