Organic extracts from five medicinal plants collected in Oman were assayed for in vitro cytotoxic property. Dried samples from latex, leaves, roots and stem bark of these species were macerated in ethanol to give crude extracts which were Kupchan's partitioned into hexane, chloroform and ethyl acetate fractions. Six different concentrations of each fraction were subjected to brine shrimp test to determine their lethality values. Percent mortalities from each fraction were then converted to LC50 values by Finney probit analysis. Chloroform and ethyl acetate extracts from Calotropis procera latex and aerial part of Rhazya stricta were the most active. LC50 values for C. procera latex were 3.0 and 8.2 μg/ml, respectively, while that of R. stricta were 18.1 and 13.9 μg/ml, respectively. C. procera and R. stricta growing in Oman are good sources of cytotoxic compounds.