A microassay was used to determine the activities of α- and β-esterases and acetyl Cholinesterase in larvae and adults of populations of Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae), in northeastern Mexico. Main collection sites were cemeteries and tire dumps. Three mechanisms of resistance were determined; however, elevated β-esterase activity was prominent, with frequencies greater than 92% in adult Asian tiger mosquitoes in three of the populations. Based on these results, we concluded that the mechanisms of resistance in the populations studied are caused mainly by esterase activity. This study can serve as a reference for future programs aimed at controlling this species.