A field experiment was conducted at Bidhan Chandra Krishi Viswavidyalaya, Mohanpur, Nadia, West Bengal during 2011-12 to study the degradation dynamics of an acetanilide herbicide alachlor in maize ecosystem. Alachlor (50% EC) was applied to the cropped soil at 2500 and 5000 g/ha at 38 days after the sowing of seed. The initial deposits of alachlor in maize leaf ranged from 0.30 - 0.39 µg/g at recommended dose and 0.61-0.65 µg/g at double dose but in maize field soil, the corresponding values were 1.23-1.31 µg/g and 2.46 to 2.52 µg/g for recommended and double dose, respectively. The alachlor residues in maize leaf were below the limit of quantification LOQ of 0.01 µg/g on 15th day after application whereas, it still persisted up to 15th day in soil samples irrespective of dose. At harvest, residues of alachlor were not observed in maize grains and soil samples. The half-life values of alachlor in maize ranged from 3.17-3.62 days irrespective of dose and substrate.