A field experiment was conducted at Visva-Bharati University under red and lateritic belt of West Bengal with the objective to evaluate the bio-efficacy of ready-mix orthosulfamuron 0.6% + pretilachlor 6% GR on weeds, yield of puddled transplanted rice (PTR) and its residual effect on succeeding crop. Four doses of ready-mix orthosulfamuron 0.6% + pretilachlor 6% GR at 40 + 400, 50 + 500, 60 + 600 and 70 + 700 g/ha, sole orthosulfamuron 50% WG at 75 g/ha, sole pretilachlor 50% EC at 750 g/ha, ready-mix bensulfuron-methyl 0.6% + pretilachlor 6% GR at 60 + 600 g/ha (check), hand weeding and unweeded control were assigned in randomized complete block design, which were replicated thrice in PTR. At 30 days after application, orthosulfamuron + pretilachlor at 60 + 600 and 70 + 700 g/ha as pre-emergence were found very effective against Panicum repens L., Monochoria vaginalis (Burm.f.) C. Presl, Alternanthera philoxeroides (Mart.) Griseb., Ludwigia parviflora Roxb., Sphenoclea zeylanica Gaertn., and Cyperus iria L. with 95-96% reduction in total weed biomass and comparable with ready-mix bensulfuron-methyl 0.6% + pretilachlor 6% GR at 60 + 600 g/ha (standard check). As compared to ready-mix orthosulfamuron + pretilachlor at 70 + 700 g/ha, sole application of pretilachlor had significantly higher infestation of P. repens, M. vaginalis, A. philoxeroides and L. parviflora. Similarly, sole orthosulfamuron also recorded higher infestation of all these weeds except L. parviflora. There was 9.4-11.0% yield advantage in rice with application of ready-mix formulation of orthosulfamuron + pretilachlor at 60 + 600 and 70 + 700 g/ha compared to sole pretilachlor and orthosulfamuron. None of the herbicides had any adverse effect on the yield of succeeding yellow sarson and on the soil microbial population.