Objective: To screen the effect of 28 medicinal plants on inhibition of pancreatic lipase and evaluate the phytochemical contents of extracts. Methods: The ethanolic extracts of 28 traditional Thai herbal medicines were assayed for their in vitro activities against porcine pancreatic lipase using p-nitrophenyl butyrate as a substrate. Quantitative estimation of flavonoids, phenolics, and alkaloids was done. Results: Extracts from four herbs, Memecylon edule Roxb., Garcinia vilersiana Pierre, Cryptolepis elegans Wall. and Phyllanthus chamaepeuce Ridl., at a concentration of 100 μg/mL, strongly inhibited porcine pancreatic lipase by 90.97%, 92.04%, 94.64% and 95.38%, respectively. There was a significant positive correlation between phenolic content and inhibition activity. Inhibition activity was significantly correlated with flavonoid and with alkaloid contents. Conclusions: From this result, it could be concluded that herbs represent a rich of anti-pancreatic lipase compounds, in particular, Cryptolepis elegans Wall. and Phyllanthus chamaepeuce Ridl. It is suggested that the phytochemical compounds from these plants may be applied for the prevention and treatment of obesity or hyperlipidemia.