Background:Urticaria is a common itchy skin condition characterized by swelling and erythema. A variety of treatments is available today. The purpose of this study was to evaluate the clinical effects of probiotic use in patients with chronic resistant urticaria.Methods:This four-way blind randomized clinical trial was conducted between June 2019 and June 2020. Study population consisted of patients with chronic urticaria who did not respond well to first line treatment with antihistamines. For the intervention group, antihistamine (cetirizine) and probiotics (femilact capsule) and for the control group, antihistamine (cetirizine) and placebo were administered twice a day for 8 weeks. The “Urticarial Activity for 7 Days” (UAS7) questionnaire was used to assess urticaria activity and the Dermatology Life Quality Index (DLQI) questionnaire was used to assess the quality of life of patients.Results:Patients’ age range was 7 to 30 years with a mean and standard deviation of 23.6±9.2 years. 31 (81.57%) cases were females and 7 (18.42%) cases were males. Twenty patients were in the intervention group and eighteen patients were in the control group. The mean scores of UAS7 questionnaire were reduced in both groups, but it was more significant in the intervention group (9.6±6.4) compared to the control group (12.7±8.1) at the end of week eight of treatment (P=0.036). Also, there was no significant difference in the quality of life between the two groups after 8 weeks (P=0.805).Conclusion:This study showed that probiotic consumption along with antihistamines significantly improved the activity of urticaria but not the quality of life of patients.