Abstract: A field experiment was conducted at the Regional Agricultural Research Station of Barisal, Bangladesh during the Kharif season of the year 2000 to find the optimum fertilizer rate for summer mungbean cv. Barimung-4 in an attempt to maximize the yield potential. In this regard, various combinations of NPK fertilizers and Rhizobium inoculation (N20P40K20 kg ha–1, P40K20 kg ha–1, N20K20 kg ha–1, N20P40 kg ha–1, N20 kg ha–1, Rhizobium + P40K20 kg ha–1, Rhizobium, and control) were imposed to the experimental plots. Results revealed that Barimung-4 produced the maximum seed (1270.21 kg ha–1) and straw yields (2434.36 kg ha–1) when the crop was fertilized with N20P40K20 kg ha–1 followed by Rhizobium + P40K20 kg ha–1 (1220.30 and 2406.14 kg ha–1, respectively. The lowest seed and straw yields were obtained from the control (887.01 and 1864.68 kg ha–1, respectively). Different plant characteristics such as plant height, branches/plant, pods/plant, pod length, seeds/pod, 1000-seed weight and harvest index increased significantly due to the application of various combinations of NPK fertilizers and Rhizobium inoculation over the control.