An investigation was carried out with a view to estimating heterosis for yield and its attributes under high temperature conditions at the experimental field of Horticulture, Department of Agriculture, Sylhet Agricultural University, Bangladesh during hot summer season (May to August) of 2013. In this study ten tomato hybrids developed from half diallel crossing fashion among five parental lines of tomato in winter season of 2012- 2013 (October 2012 to February 2013). These ten tomato hybrids along with five parental lines were evaluated under RCB design with three replications to estimate better parent heterosis for ten characters. Significant better parent heterosis was found for all characters except days to first harvest. The maximum better parent heterosis for number of fruits per plant was observed for the cross combination of C51 × C71 (85.12%) followed by C41 × C11 (67.10%). The highest heterosis for individual fruit weight was recorded (69.31%) from FP5 × C71 indicating this combination is important for improvement of individual fruit weight of heat tolerant tomato. The highest positive significant heterosis for pericarp thickness was found for the cross combination of C41 × C71 (60%) followed by C11 × C71 (46.25%). Positive and significant heterosis for TSS (%) was estimated from the cross C11 × FP5 (8.7%). All the cross combinations showed positive and significant heterobeltiotic effect for fruit yield per plant of which C41 × FP5 exhibited the highest heterosis (203.22%) closely followed by C41 × C51 (183.33%). Therefore, this two cross combinations can be taken for further evaluation under high temperature condition for recommending summer season cultivation in Bangladesh.