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Photoperiod and temperature are two important environmental factors affecting vegetative growth and yield of rice. The varietal diversity based on the response to temperature and photoperiod during vegetative growth was determined in a core collection of 40 Sri Lankan traditional rice accessions (SLTRA) and 2 improved and 2 wild rice types in terms of days to fully expansion of fifth leaf (DFL) and plant height (PH). Short day (SD), day neutral (DN) and long day (LD) conditions were imposed during 2 trials of high temperature (HT) and low temperature (LT) at 36.9 +/- 0.43 degrees C and 34.0 +/- 0.98 degrees C under natural temperature fluctuation. Average DFL of the collection at HT was significantly lower than that of the LT irrespective of photoperiods. Temperature affected the DFL of 22 accessions, while photoperiod alone affected 1 accession. Average PHs under HT were similar irrespective of the photoperiod, which were lower than those of LT. PH of 15 accessions was not affected by photoperiod or temperature. Temperature alone affected 12 accessions and photoperiod alone affected 2 accessions. Both photoperiod and temperature affected 4 accessions. In the cluster analysis on response to photoperiod and temperature, SLTRA and improved rice were differentiated into 2 clusters at a rescaled distance of 25. Further, sub-clusters grouped several accessions of the same variety together. The differential varietal response to photoperiod and temperature in SLTRA would be useful in breeding for climate change adaptations after further experiments on flowering time and yield.