The resistance levels of six barley (Hordeum vulgare L.) entries namely B-00080, NRB-37, V-8, Haider-93, B-99036 and JAU-87 of 2003-04 National Uniform Barley Yield Trial (NUBYT) were evaluated against the aphid, Rhopalosiphum padi (L.). Evaluation was done by seedling bulk test method for finding out resistant, moderately resistant and susceptible entries. The entry B-99036 was found to be resistant. Further studies were conducted to determine the mechanisms of resistance like antixenosis, antibiosis and tolerance. Results indicated that the entry B-00080 had antibiosis and B-99036 was the tolerant one. So, on the basis of present studies the entry having high level of resistance against R. padi (B-99036) should be incorporated in the future breeding programmes.