Abstract. L-arginine is an important factor in several physiological and biochemical processes. Recently, scientists studied L-arginine effect on inflammatory mediators such as C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). We conducted a systematic review on randomized controlled trials assessing L-arginine effect on inflammatory mediators. We searched data bases including Google scholar, ISI web of science, SCOPUS, and PubMed/Medline up to April 2019. Randomized clinical trials assessing the effect of L-arginine on inflammatory mediators in human adults were included. Our search retrieved eleven articles with 387 participants. Five articles were on patients with cancer and 6 articles were on adults without cancer. L-arginine was applied in enteral form in 5 articles and in oral form in 6 articles. Eight articles were on both genders, two articles were on women, and one article was on men. L-arginine could not reduce inflammatory mediators among patients with and without cancer except one article which indicated that taking L-arginine for 6 months decreased IL-6 among cardiopathic nondiabetic patients. Our results indicated that L-arginine might not be able to reduce selected inflammatory mediators, but for making a firm decision more studies are needed to be conducted with longer intervention duration, separately on male and female and with different doses of L-arginine.