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The experiment comprising of mechanical transplanting of 3, 4 and 5 weeks-old seedlings was conducted at Punjab Agricultural University, Ludhiana during 2010 and 2011 to study the effect of seedling age on heat utilization, radiation interception and productivity of rice. Mechanical transplanting of 3 weeksold seedlings recorded highest accumulation of growing degree days (GDD) of 2045oC day resulting from highest number of days taken to maturity. The heat use efficiency (HUE) was similar in all transplanted seedlings. The growth and yield attributes in terms of plant height, tiller number, panicle length, panicle weight, leaf area index (LAI) and photosynthetically active radiation (PAR) interception by the crop declined with increasing seedling age from 3 to 5 weeks. The 3 weeks-old transplanted seedlings recorded 0.90 and 2.79 per cent higher grain yield over 4 and 5 weeks old seedlings, respectively although the differences were non-significant.