The experiment was conducted at the experimental field of Bangladesh Institute of Nuclear Agriculture, Mymensingh, Bangladesh from the month of March to May 2011 to investigate the effect of cultivars and seed rates on morpho-physiological characters, yield components and yield of summer mungbean [Vigna radiata (L.) Wilczek]. The experiment comprised three types of varieties viz., BINAmung-6 (bold seeded), BINAmung-7 (small seeded) and BINAmung-8 (medium seeded) and three seed rates viz., 30, 40 and 50 kg ha-1. The experiment was laid out in a two factor randomized complete block design with three replications. Number of branches plant-1, leaf area plant-1, total dry mass plant-1, relative growth rate, pod number plant-1, seed and biological yield plant-1 and harvest index decreased with increasing seed rate while reverse trend was observed in plant height and leaf area index. Results revealed that optimum seed rate of a mungbean variety depended on seed size. The variety having smaller size seeds require lower seed rate and vice versa. On an average over the varieties, the seed rate 40 kg ha-1 resulted in the highest seed yield in mungbean. The optimum seed rate for maximizing seed yield of bold seeded variety, BINAmung-6 was 50 kg ha-1. Similarly, the optimum seed rate for small seeded variety, BINAmung-7 and medium seeded variety, BINAmung-8 was 30 and 40 kg ha-1, respectively. The dry matter partitioning to economic yield was also higher at above optimum seed rates of the varieties. Among the varieties, BINAmung-8 produced the highest seed yield both per plant and per hectare due to its favourable dry matter partitioning to economic yield.