Doramectin, a novel avermectin, is widely used as a potent endectocide. There are evidences which show that doramectin has effects on the central nervous system of the animals, since it affects GABA sensitive neurons. The present study was conducted to examine the pharmacodynamic interactions that may result from concurrent administration of doramectin and acepromazine, a tranquillizer. In this experimental study, the effect of doramectin on the activity of acepromazine was assessed by employing Spontaneous locomotor activity test, Forced locomotor activity test, Traction wire test, Conditioned response avoidance test and aggregation toxicity. In spontaneous locomotor activity test it was found that doramectin potentiated the activity of acepromozine but it was not significant. In forced locomotor activity test and traction wire test it revealed that doramectin attenuated the activity of acepromazine but again not significant. The result of conditioned response avoidance test and aggregation toxicity test showed that doramectin did not alter the activity of acepromazine. Thus, the results obtained in the present study suggest that doramectin doesn’t affect the pharmacologic activity of acepramozine. This could be attributed to the difference in the mechanism of action of the two drugs in the central nervous system.