Abstract: To find out highly resistant varieties of rapeseed-mustard, sixty-five cultivars (brown sarson-1, Indian mustard-42, gobhi sarson-4, kiran rai-4, taramera-2, toria-5 and yellow sarson-7) were screened against mustard aphid, Lipaphis erysimi during winter season of 2005-06 and 2006-07. The findings revealed that aphid commenced their attack 7 Weeks After Sowing (WAS) and reached to a maximum level at 14 WAS on October 25 (timely) sown cultivars. Whereas, on November 10 and 25 seeded cultivars, aphid incidence was initially recorded on 6 WAS and 4 WAS, which reached to a maximum at 13 and 11 WAS, respectively. The timely sown (October 25) cultivars escaped the aphid infestation and exhibited better growth due to stored moisture by plant and also minimum aphid load than late seeded (November, 10 and 25) cultivars. While calculating Mean Aphid Infestation Index (MAII), it remained below 1.00 on Kranti, Maya, MYSL-203, PCR-7 and Pusa Agrani (Indian mustard); Pusa Swarnim (Kiran rai) and NDYS-2, YST-151 (yellow sarson) when cultivars seeded on October 25 and November 10. Therefore, these cultivars could safely be placed under highly resistant category. Among late sown rapeseed-mustard (November 25), no cultivars found as highly resistant, though, cultivars showing high tolerance during timely sowing become moderately resistant on account of their late (November 25) sowing. Interestingly, gobhi sarson and kiran rai showed relatively less damage due to their late flowering and different plant texture than other cultivars.