Background: Rosemary is widely found along the coasts of the Mediterranean Sea. Its leaves or extract were found to have a high antioxidant and anti-inflammatory activity. It is also used as an antispasmodic, analgesic, anti-rheumatic and expectorant. These actions are mainly due to its content of essential oils. Azathioprine (AZA) is an immunosuppressive drug. It is widely used in many diseases. A major drawback is the occurrence of side-effects, especially acute pancreatitis.   Aim of the work: This work was done to study the effect of dietary supplement of rosemary leaves as a strategy for amelioration of the side-effects of azathioprine.   Material and Methods: Thirty-two adult male albino rats were used in this study. They were equally divided into four groups. Group I: control group, group II: rosemary group, the animals were given a daily oral dose of rosemary leaves extract. Group III: azathioprine group, the animals were given a single dose of AZA intraperitoneally. Group IV: rosemary azathioprine group: the rats were given daily doses of rosemary leaves extract then azathioprine in the last day of the experiment as in the previous regimen. The experiment continued for ten days. Blood samples were taken from all groups and examined for tumour necrosis factor alpha, serum amylase enzyme, C-reactive protein and renal function tests (serum urea and creatinine).   Results: Rosemary significantly decreased the levels of tumour necrosis factor alpha, serum amylase enzyme and serum urea and C-reactive protein in rosemary AZA group compared to AZA group .   Conclusion: The aqueous rosemary leaves extract has the ability to ameliorate the biochemical pathways of the side-effects of azathioprine, so it is advisable to give it concomitantly to patients treated by azathioprine.