An insight knowledge nature and relative magnitude of gene actions involved and combining ability is useful for a breeder to assess nicking ability in self-pollinated crops. In this connection, an attempt was made to estimate the gene action and combining ability of 70 newly developed CMS based heterotic rice hybrids developed from ten newly developed CMS lines and seven testers were evaluated for grain yield and its components at Hybrid rice scheme, ZARS, V. C. Farm, Mandya. Among the lines, CMS 2 had significant gca effects at 1% level of significance in desired direction for four traits viz., panicle weight, pollen fertility, spikelet fertility and number of spikelets per panicle. Out of seven testers, KMR 3 found to be good general combiner for five traits viz., days to 50 per cent flowering, plant height, number of tillers per plant, number of panicles per plant and grain L/B ratio. Among the 70 hybrids, CMS1 × KMR3 was good specific combiner for grain yield per plant and grain L/B ratio. It further revealed that SCA variances were higher than the GCA variances for all the characters which indicated preponderance of non-additive gene action. Hence, CMS 2 and KMR 3 are identified as promising lines which can be used in further breeding programme. [ABSTRACT FROM AUTHOR]