Four summer rice cultivars, viz. Jyotiprasad, Bishnuprasad, Joymoti and Kolaboro were grown in the farmers field at Kohar Goan, Jorhat during 2004-05. Four different treatments given to 40 days old seedlings before transplanting were control, 40 C cold hardening treatment in light for 48 hours, GA3-10 ppm treatment five days before transplanting and ABA-10 ppm treatment five days before transplanting. Various morphological and physiological parameters, viz plant height, tiller number, leaf number, leaf area, relative leaf water content, leaf chlorophyll, nitrogen, phosphorus and potash content of shoot at harvest were significantly influenced by the treatments. Seedlings treated with GA3 exhibited better growth and plant vigour in comparison to control. Bio-chemical traits, viz leaf proline content, total soluble sugar in stem, grain yield and yield attributes such as panicle length, grains panicle^-1, sterility percentage were also found to be influenced significantly due to GA3, ABA and 40 C hardening treatment. The adverse effect of low temperature on growth and development of summer rice can be reduced with suitable cold hardening treatments. Among the different treatments GA3 was found to be the most suitable treatment for improvement of cold tolerance in terms of growth and yield in summer rice.