Abstract: Acetylcholinesterase (AChE) was purified from the brain tissues of topmouth gudgeon (Pseudorasbora parva) by PEG2000/phosphate salt two phases extraction, DEAE-Sephadex A-50 and Sephadex G-200 chromatography. The comparative study of kinetic characters and resistance to inhibition by malaoxon and triazophos between crude and purified AChE from topmouth gudgeon was done. The result suggested that purified AChE is pure after the purification procedures; and the affinity of the brain AChE in purified state to substrate was no significantly different with that in crude state, while the inhibition of purified AChE to substrate was more sensitive than that of crude AChE; it was found in inhibition study that the sensitivity of purified AChE to both oxidized malathion and oxidized triazophos were significantly heigher than that of crude AChE.