Abstract: Cashew plant (Anacardium occidentale L.) is a crop producing cashew nut shell that contain phenolic compounds such as lacquer oil (cashew nut shell liquid) which can be used for many studies. This study was conducted to determine the potency of acute toxicity (LD50) of cashew nut shell extract on female albino Wistar rats using Weil method. Twenty rats used in this study. The rats was divided into five groups, each consist of four rats after acclimatization. Each group was given the extract of cashew nut shell orally (force-fed). The amount of cashew nut shell extract that were given to group I, II, III and IV were 2.5, 25, 250 and 2,500 mg kg–1 b.wt., respectively, while group V were given 0.5% sodium carboxyl methyl cellulose (CMCNa) solution. Clinical symptoms were observed 24 h after the administration of extract include behavioral changes i.e., licking, scratching, twitching, tremors, wrihing, reactivity to stimuli, cerebral and spinal reflexes, secretions, breath, skin, hair and death. Probit analysis using Weil method was used as an effective dose. The results showed that the potency for acute toxicity (LD50) of cashew nut shell extract was 2,018 mg kg–1 which classified as moderately toxic category. The administration of extract also causes behavioral changes in animal including passivity and mucus secretion. All doses of the extract did not affect the development body weight and the weight of organs (spleen, liver, heart, kidneys and lungs) in female rats.