The conventional manual weed management is one of the labour intensive and expensive operation in crop production as it involves low efficiency, time consuming, human drudgery and higher cost of operation. The use of self-propelled rotary weeder for mechanical weeding reduces the drudgery and ensures a comfortable posture of operator or farmer during weeding operation. Hence, a self-propelled narrow crop rotary weeder was developed by department of Farm Machinery & Power Engineering, COAE&T, CCS HAU, Hisar during the winter (Rabi) season of 2016 and was evaluated for its performance in mustard crop having row to row spacing of 45 cm. Three forward speeds (1.6, 1.8 and 2 km/h), two blade lengths (180 and 195 mm) and three speeds of rotor (330, 360 and 390 rpm) were selected for its evaluation and results were compared with manual hand weeding using Kasola (tool smaller than spadi in size). The effective field capacity of 0.09 ha/h, field efficiency of 67.98%, weeding efficiency of 80.12% and plant damage of 2.9% were observed at the best combination of operational variables i.e. rotor speed of 360 rpm, blade length of 180 mm and forward speed of 1.6 km/h. The labour requirement with rotary weeder was reduced to 11.11 man-h/ha when compared to 160 man-h/ha for manual hand weeding. Thus, rotary weeder saved 93% of labour and 75.45% of cost of operation in comparison to manual hand weeding using Kasola in mustard crop.