To determine the relative role of weather variables on mustard aphid Lipaphis erysimi (Kalt) population, field experiments were conducted. The study revealed that in early sown Indian mustard, the aphid population had a significant negative correlation with minimum and maximum temperature. Similarly, the morning and evening RH, and rainfall showed negative correlation with aphid population. On division of aphid infestation period into three different phases of infestation, it was observed that during the establishment phase, the weather parameters had significant role in governing the aphid population. The temperature, rainfall and sunshine hours were negatively correlated, whereas, morning and evening relative humidity and wind speed showed positive correlation. During the declining phase, wind speed alongwith temperature had negative relationship with aphid population build up.