In this study, it was aimed to investigate the effects of thymoquinone (TQ), which is the bioactive phytochemical constituent of the seeds oil of Nigella sativa, on somatostatin secretion in the rat pancreatic tissue by immunohistochemical method. Animals (n=30) were divided into 3 groups as follows: control, sham and thymoquinone. While Thymoquinone group received 8 mg/kg of TQ which injected for 14 days, only isotonic saline was injected to the sham group for same time. The control group received nothing. Crossman"s triple staining was applied to tissue sections to examine histology. Streptavidin-Biotin-Peroxidase Complex method was used to investigate somatostatin immunoreactivity in the pancreatic tissue. Specific somatostatin immunoreactivities were observed in endocrine cells (islets of Langerhans) in all groups. It was determined that somatostatin secretion increased in the thymoquinone group compared to control and sham. In conclusion, thymoquinone administration was concluded to increase the secretion of somatostatin that is known to regulate certain hormones such as growth hormone, insulin, glucagon, secretin and gastrin.