The present study aims to investigate the effect of some herbal extract such as phenolic compounds on the viability of Leishmania tropica promastigotes in vitro. Four tested chemical agents (caffeic acid (CA), ferulic acid (FA), syringic acid (SA) and 4-hydroxybenzoic acid (4-HBA)) were used in this study. The viability of Leishmania tropica promastigotes was investigated under five different concentrations (10, 15, 20, 25 and 30 mg/ml) of each agent after (72 h). CA was the most active agent on the promastigotes viability after 72 h exposure to 30 mg/ml concentration so that the parasiticidal effect reach (53 9 10 4 ) promastigote/ml. FA is the second agent in parasiticidal effect that parasiticidal effect reach to (50 9 10 4 promastigote/ml) at a concentration (30 mg/ml), 4-HBA is the third agent in parasiticidal effect that reach to (48 9 10 4 promastigote/ml) at a concentration (30 mg/ml), SA is the weakest agent in parasiticidal activity that reach to (44 9 10 4 promastigote/ml) at a concentration (30 mg/ml). It can be concluded that (CA, FA, SA and 4-HBA) possess acidal effect on the Leishmania tropica promastigotes in vitro.