Four species of Brassica viz,. B. napus, B. juncea. B. compestris and B. rapa were studied for their relative resistance/susceptibility against aphids, under field conditions for three consecutive crop seasons i.e., 2009-2010, 2010-2011 and 2011-2012. The data on the incidence of aphids were recorded at weekly interval. Host plant susceptibility indices were also calculated. B. napus was found to be susceptible showing maximum population of aphids i.e., 6.80 per 10-cm inflorescence whereas B. compestris showed comparatively resistant response with minimum population of aphids i.e., 0.43 per 10-cm inflorescence. The population of aphid was recorded to be the highest (12.83 per 10-cm inflorescence) on March 11 which showed non-significant difference with those of recorded on March 04 (12.52/10-cm inflorescence) Furthermore, the population of aphids remained present throughout the crop season starting from December 10 of each cropping period. The population of aphids was recorded to be higher on B. napus and B. juncea as compared to B. compestris and B. rapa on most of the dates of observation. Non-significant difference was found to exist among years regarding the population of aphids on Brassica species. The population of aphids showed significant difference among years for B. napus whereas B. juncea, B. compestris and B. rapa showed non-significant difference. The crop seasons 2009-2010, 2010-2011 and 2011-2012 did not show significant difference regarding the population of aphids at various dates of observation starting from December 03 to January 28 for each crop season. Significant difference was found to exist thereafter from February 04 to march 25 among crop seasons. The highest population was recorded to be 12.84 during 2009-2010 on March 11, 13.15 per 10-cm inflorescence on March 04 during 2010-2011 and 13.78 per 10-cm inflorescence on March during 2011-2012. The maximum HPSIs were recorded to be 51, 48, 55 and 51 percent in B. napus during 2009-2010, 2010-2011, 2011-2012 on cumulative basis, respectively and proved to be susceptible specie. The minimum HPSI was recorded to be 3, 5, 1 and 3 percent for B. compestris during the crop seasons as mentioned above, respectively and found to be comparatively resistant.