Organophosphate inhibits carboxylesterase thus regular treatment includes carboxylesterase oxime reactivator in combination with anti-muscarinic agents. In order to progress the understanding of species differences and to enable an additional reliable extrapolation of animal result to quail a study was initiated to inspect the effect of insecticide compounds, that is, mevinphos, ethoprop, and fenthion, with quail-serum carboxylesterase and common chicken-carboxylesterase. The rate constants for the inhibition of carboxylesterase by these organophosphate and for the aging and spontaneous reactivation of organophosphate-inhibited carboxylesterase enzyme as well as for the oxime-induced reactivation of organophosphate-inhibited carboxylesterase enzyme by the oximes trimedoxime, methoxime, N,N′-(ethano)bis(4-hydroxyiminomethyl)pyridinium methanosulphonate, HI-6, and HLö-7 were determined in this study. Compared to quail-serum carboxylesterase and chick-carboxylesterase displayed a lower sensitivity toward the inspected organophosphate. Furthermore, a slower aging and spontaneous reactivation of quail-serum carboxylesterase enzyme was recorded. The potency of the detected oxime reactivator was remarkably lower with organophosphate-inhibited quail-serum carboxylesterase.