This study was conducted to determine the changes in physiological and some biochemical responses of selected rainfed lowland rice genotypes under drought condition. AL-108, AL-87, AL-97, AL-55 and AL-5, initially selected based on evaluation during germination and seedling stages; and NSIC Rc14 (tolerant check) PSB Rc82 (moderately susceptible check) were evaluated under drought and well-watered condition from 20 DAS and 30 DAS for a period of 12 days. Varying tolerance in terms of physiological and biochemical traits under different period of drought imposition were observed in different genotypes. All of the test genotypes had high photosynthetic efficiency under drought although some biochemical responses differed.Relative water content, stomatal conductance, transpiration rate and photosynthetic rate were reduced in all test genotypes but more severe reduction was observed in susceptible check (PSB Rc82). Transpiration rate was minimal in tolerant genotypes (NSIC Rc14). Total chlorophyll and carotenoids decreased under drought in most the genotypes, except for AL-108, AL-5 and AL- 97. Concomitantly, the amount of antioxidant and total soluble sugar in the drought-tolerant genotypes increased markedly during drought stress, while decreased in susceptible variety. It can be concluded that maintenance of relative water content and photosynthetic efficiency, and increase in antioxidant level and total soluble sugar accumulation, were associated with the drought tolerance of the rainfed lowland rice varieties.