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In the present investigation,the alkaloid extracts obtained from leaves of Avicennia marina were isolated by Sephadex LH-20 column chromatography at 0.7mL/min velocity using methanol as mobile phase,two isolated compounds Ⅰand Ⅱ were furnished.Moreover the crude alkaloid extracts,the isolated compounds Ⅰand Ⅱ were evaluated for acetylcholinesterase inhibition activities in vitro and the inhibition ratio reached 59.33±0.58﹪,71.67±0.33﹪,and 76.00±0.35﹪at a concentration of 70μg/mL,respectively,which may be novel acetylcholinesterase inhibitors of potential in the therapy of Alzheimers disease.At last the inhibition kinetics of the isolated compound II analyzed by Lineweaver-Burk plots due to the highest acetylcholinesterase inhibition activity.The results revealed that the Michaelis-Menten constant Km and Vmax were found to be 0.268±0.033μg/L and 3.345±0.047 U,these values were increased by 23.50% and decreased by 37.92% in the presences of the isolation,respectively.In addition,the values of mixed inhibition constant Ki and K′i was 7.173±0.087μg/L and 8.728±0.065μg/L,respectively.