An attempt has been made to quantify the effect of weather parameters and ladybird beetle on population fluctuation of aphid using path analysis of data collected during rabi 2012-13 and 2013-14 at Junagadh Agricultural University, Junagadh. The result revealed that the direct effect of minimum and maximum temperatures on aphid population was negative and low (-0.4939 and -0.2628, respectively) while it was positive and moderate (0.5443) by mean temperature. The direct effect of morning relative humidity was positive and very high (1.8615), while mean relative humidity exhibited negatively very high direct effect (-3.3158) on aphid population. Residual value indicated that all these biotic and abiotic factors had a total combined effect of 86.01 per cent on population build-up of mustard aphid. It indicated that only 13.99 per cent effect was through other unknown factors existing in the ecosystem during both seasons.