Abstract: The natural appearance of mustard aphid on Brassica germplasm was observed on 11th January (60 DAS) and disappeared after 2nd March (110 DAS). The peak aphid population was found at a maximum, minimum and average temperature of 23.37°, 6.87° and 15.76°C, respectively and mean relative humidity of 54.75% on 10th February at 90 DAS. Then, decline in aphid population and simultaneously increase of Coccinella was at 100 and 110 DAS, respectively. Maximum and average temperature showed as positively non-significant effect while minimum temperature caused negatively non-significant on the population of aphid. However, relative humidity had a negative effect. Late appearance of Coccinella too could not have any regulatory effect on the incidence of this pest.