Weeds in crop fields are largely influenced by crop rotations and management practices. A better understanding of response of various weed species to changing management practices is required to develop improved weed management systems.  A study was conducted to assess the effect of different tillage intensities and crop rotations on the weed population dynamics in rice-based cropping systems. In this study, three tillage practices viz. conventional tillage (CT), reduced tillage (RT) and RT with 30% crop residues (RTR30) were evaluated in three different crop rotations, viz. rice-wheat, rice-lentil and rice-winter maize for their effect on weeds. Results show that weed density and species composition differed with tillage and crop rotation. Interaction between various tillage intensities and cropping systems had significant effect on density and dry weight of total, broadleaved, grasses and sedges. Irrespective of the tillage systems rice-wheat crop rotation favoured the prevalence of weeds (a total weed population of 1670/m2 and weed dry biomass of 241.1 g/m2), whereas rice-winter maize rotation suppressed the weed growth (a total weed population of 403/m2 and weed dry biomass of 213.4 g/m2) in summer (pre-Kharif) season. Reduced tillage with 30% residues retention (RTR30) favoured the infestation of horse purslane (Trianthema portulacastrum L.) in rice-wheat cropping system, but suppressed the weed growth in rice-lentil system. Contrary to this, RTR30 favoured the infestation of black nightshade (Solanum nigrum L.) in rice-winter maize cropping system, but suppressed the weed growth in rice-lentil and rice-wheat systems during winter season.