Context: Acacia catechu is a tree which possesses lots of therapeutic value. Objective: To evaluate the lethality assay of Acacia catechu seed using Invitro parameter. Background: Acacia catechu willd is an indigenous plant having tremendous medicinal properties and well reviewed in literature. Ethanolic extract of Acacia catechu sed has already been reported to possess selected pharmacological activities like anti diabetic,but there are no reports on cytotoxicity assay of this extract. Methods: Twenty nauplii were added into three replicates of each concentration of the plant extract. After 24,48 hours, the surviving brine shrimps were counted and percentage of mortality was assessed Results: The present study reveals that Acacia catechu possess significant cytotoxic activity when tested in vitro. Conclusion: From the present study it can be concluded that ethanolic seed extract of Acacia catechu possessed marked cytotoxic effect The effect was plausibly due to the presence of phytochemical contents present in it. Clinical significance: Novel cytotoxic, pesticidal compounds can be isolated from plant based sources through the investigation of cytotoxic activity against brine shrimps