A field experiment was conducted in rabi season 2018-19 and 2019-20 at Research farm of Bihar Agricultural College, Sabour with the aim to find out the effect of nutrient and weed management on grain yield, WCE and economics of mustard. This experiment consisted of three nutrient levels (N1-soil test-based, N2-100 % RDF, N3-125 % RDF) in main plot while eight weed management practices (W1-Weedy, W2-HW, W3-pendimethalin, W4-pendimethalin fb quizalofop, W5-pendimethalin fb clodinafop, W6-oxyflourfen, W7-oxyflourfen fb quizalofop, W8-oxyflourfen fb clodinafop) in sub plots, laid out in split plot design replicated thrice. Results indicated that pendimethalin 30 EC 1.0 kg a.i. ha-1 PE fb quizalofop 5 EC 60 g a.i. ha-1 PoE + 125% RDF (N3W4) exhibited highest WCE (85.66 and 88.83 %) in 2018-19 and 2019-20, respectively being at par with N3W5 (81.84 %) in 2018-19 only. Though HW at 25 and 50 DAS + 125% RDF (N3W2) recorded highest WCE (100 %) than weedy. Grain yield was maximum (18.63 and 17.78 q ha-1) under N3W4 being at par with N3W7 in 2018-19; while in 2019-20, it was at par with rest of the treatments except N3W1 and N3W6. In 2018-19, N3W4 noted highest net return (Rs. 59068 ha-1) being at par with N3W2 and N3W7. While in 2019-20, same treatment exhibited highest net return (Rs. 58279 ha-1) being at par with rest of the treatments except N3W6 and N3W1. In 2018-19, N3W4 recorded highest B: C ratio (2.78) being at par with rest of the treatments except N3W2 and N3W1. In 2019-20, N3W7 exhibited highest B: C ratio (2.80) being at par with rest of the treatments except N3W6 and N3W1.