The interaction of Syrphid predator Episurphus baltatus with the population density of green peach aphid Myzus persicae of Brassica campestris L. grown in four fields of Hyderabad was studied during Rabi season i.e. November 2015 to March 2016. Adult hoverflies were collected by three standardized methods, Aerial netting through insect hand net, Yellow pan water trap and Malaise trap. However, larvae were directly collected from leaves, stem, growing points and inflorescence of Brassica plant. Monthly population dynamics revealed that the occurrence of Episurphus baltatus started from the 3rd week of November and attended its peak density in the 2nd week of February, which coincided with the highest density of aphids. The numerical density of Episurphus baltatus determined a rise in response to abundance of aphids in the field, whereas the environmental factors also influenced the density of predator. The Pearson’s correlation analysis revealed a strong positive correlation of predator with prey aphid r=.895, p=.01 and a moderate positive correlation with relative humidity 0.562, p=.05. Nonetheless, rainfall and temperature were negatively correlated (r=-0.647 and r=-0.597 respectively) with predator population density in Brassica ecosystem. In addition, regression analysis suggested that aphid density (prey) has high effect (58.3%) on predator population. The temperature and rainfall showed a moderate and low negative effect (-32.0% and -15.1% respectively) on predator; whereas, relative humidity indicated very low positive effect (9.3%) on predator density.