¹Department of Pharmacy, Faculty of Medicine and Health Sciences, An-Najah National University, Nablus, Palestine DOI : 10.12991/mpj.2017.9 Plants are used to the treatment and prevention of many of metabolic, degenerative and cardiovascular diseases. Obesity is one of the most common metabolic diseases which is considered one of the global health problems. The present study aimed to screen anti-lipase effect of Portulaca oleracea, Urtica urens, Brassica napus and Lathyrus hierosolymitanus traditional Palestinian medicinal wild plants. Anti-lipase activity was measured by using porcine pancreatic lipase inhibitory test which was established by using the UV-visible spectrophotometer method, while orlistat (anti-obesity drug) was used as a positive control reference. The porcine pancreatic lipase inhibitory effect for organic and aqueous extracts of Urtica urens were 157 μg/ml and 157.1 μg/ml, respectively. While the anti-lipase IC₅₀ value for the organic extract of P. oleracea was 262.03 μg/ml. In addition, the aqueous extracts of Brassica napus and Portulaca oleracea have anti-lipase activity with the IC₅₀ values 296.87 μg/ml and 417.62 μg/ml, respectively. Meanwhile, Lathyrus hierosolymitanus both aqueous and organic extracts were almost inactive. The results showed that Urtica urens, Portulaca oleracea, and Brassica napus have anti-lipase activity, which provided evidence for their folkloric use as functional food and medicine. These three plants could be used as antilipase agents in the pharmaceutical and nutritional industries or may be used as fatty food additives in order to decrease the absorption and digestion of fats from food. Keywords : Obesity, pancreatic lipase enzyme, traditional plants