The present investigation was carried out with a view to study the magnitude of heterosis, combining ability and gene action through half diallel analysis involving eight parents and their twenty eight F1s in tomato. The experimental material was planted in Randomized Block Design with three replications at College Farm, N.M. College of Agriculture, Navsari Agric. University, Navsari during rabi 2013-14. Combining ability analysis revealed that the mean squares due to general combining ability and specific combining ability were highly significant for almost all the traits indicating importance of both additive as well as non-additive gene effects in the expression of all the traits. However, the variances due to general combining ability were lower than specific combining ability for all traits thus ratio of 2GCA and 2SCA pointing out the preponderance of non-additive gene effects for the traits studied. The general combining ability effects revealed that AT-3, GT-2 Vybhav and Flordade were the good general combiners for fruit yield. The crosses DVRT-2 x IIHR 2195, AT-3 x JT-3 and JT-3 x DVRT-2 were found to be good in respect of SCA effects for fruit yield per plant and involved poor x poor, good x good and good x poor. This might be due to effect of alleles of combining parents. Out of these best specific cross combinations, majority of the crosses showed high per se performance along with higher heterotic effects and higher SCA effects for fruit yield per plant indicating more reliability of per se performance. The per se performance of parents were more or less related to their GCA effects.