Cotton (Gossypium hirsutum L.) is one of the important cash crops. Among all the environmental stresses high temperature is a key factor responsible for reduction in growth and yield of cotton. Therefore, it is important to evaluate the plant responses to heat stresses and their underlying physiological mechanisms, as it can provide insights into how plants could be modified to increase tolerance. Selenium plays a protective role in antioxidative defense mechanisms of plants while ascorbate is a major metabolite in plants and may perform a critical role in plant protection against several environmental stresses. The present investigations were carried out to improve heat tolerance in cotton by using selenium or ascorbic acid. Two independent experiments were planted during 2013 and repeated during 2014 at the Agronomic Research Area, University of Agricultural Faisalabad, Pakistan. These experiments were managed under randomized complete block design with split plot arrangement with three replicates. Seed of Bt cotton (cv. MNH-886) was used at the rate of 20 kg ha-1 and was sown at 30 cm distance from each other on 75 cm apart ridges. The plot size was 6.0 × 3.75 m. First experiment comprised of heat stress imposition (H0= No heat imposition, H1= Heat imposition at square initiation, H2= Heat imposition at flower initiation) and levels of foliar applied selenium (Se0= control (water spray), Se1= 50 mg L-1, Se2= 100 mg L-1, Se3= 150 mg L-1). In second experiment same heat stress treatments were combined with four levels of foliar applied ascorbic acid (A0= control (water spray), A1= 20 mg L-1, A2= 40 mg L-1 and A3= 60 mg L-1). The results showed that heat stress badly affected the crop osmotic potential, total chlorophyll contents and activities of enzymatic antioxidants that not only reduced the growth and yield but also resulted in poor quality fiber. Application of selenium (150 mg L-1) or ascorbic acid (40 mg L-1) improved seed cotton yield and fiber quality traits of the crop by ameliorating the negative impacts of heat on crop. The activities of antioxidants enzymes (POD, CAT and SOD) were also increased at this level of selenium or ascorbic acid. So foliar applied selenium and ascorbic acid, at their appropriate levels have potential to ameliorate the harmful impacts of heat stress and improve the performance of cotton crop.