Background & Aim: St John's wort (Hypericum perforatum L.) contains hypericin and hyperforin as the main components of the extract that binds with GABA and sigma opioid receptors. This herb has many pharmacological effects, including analgesic, sedative, soothing, antispasmodic, anticonvulsant, anti-depressant, and anti-bacteria. In this study examined the effect of two concentrations of Hypericum perforatum extract on digestive organs morphometric in male Wistar rats. Experimental: Among the 54 rats tested with six repetitions, effect of Hypericum perforatum extract was assessed in three groups. Experimental treatments were control (receiving water), groups two and three that received Hypericum perforatum extract (250 and 500 mg /kg.bw) respectively. Rats were treated with Hypericum perforatum for 03days, through the Gavage method Results & Discussion: Results indicated that big intestine weight in the 250 mg/kg.bw Hypericum perforatum treatment significantly was more than the control group (p ≤ 0.05), and also the length of big intestine was taller in 250 and 500 mg/kg.bw treatments than control group (p ≤ 0.05). Recommended application: According to results, the extract of Hypericum perforatum can use for weight increasing. تفاصيل المقالة