A field experiment was conducted during Kharif seasons of 2014-15 and 2015-16 at Bidhan Chandra Krishi Viswavidyalaya (BCKV), West Bengal to evaluate the effect of pretilachlor 50% EC on growth of composite weed flora and productivity of winter (Kharif) rice (Oryza sativa L.). The experiment comprised of eight treatments following a randomized block design with three replications. Experimental findings revealed that hand weeding twice at 15 and 30 DAT effectively controlled the grasses, sedges and broad-leaved weeds, which recorded statistical parity with the application of pretilachlor 50% EC at 750 g/ha followed by its lower dose at 600 g/ha. Grain yield losses amounted to 31.4-50.1% due to uncontrolled weed growth as compared to different weed control treatments. Among the different herbicidal treatments, pretilachlor 50% EC at 750 and 600 g/ha recorded higher weed control efficiency, yield attributes and grain yield (4.25 and 4.20 t/ha, respectively) of rice, which did not affect the germination and seed yield of succeeding lentil crop during both the years. Besides, soil beneficial microflora was not negatively influenced in long run. Considering bio-efficacy, economics and microbial study, pretilachlor 50% EC at 600 g/ha could be a better alternative for weed management and may be recommended for obtaining a higher yield of transplanted winter rice in the Gangetic Inceptisol of West Bengal.