We analyzed the morphology, growth and stress resistance traits of rice seedlings under PEG6000 treatment to explore the effect of BCAT4 on the response to drought stress, using the wildtype ‘Nipponbare’ (NIP) and mutant bcat41 as materials. The results showed that: (1) after 20% PEG treatment, the expression level of BCAT4 in wildtype NIP seedling leaves was significantly higher than that of the control, and the survival rate after rehydration was significantly higher than that of mutant bcat41. (2) After 20% PEG treatment, the relative contents of chlorophyll were decreased, the contents of proline and soluble sugar were increased, while the activities of antioxidant enzymes were increased first and then decreased in the leaves of both rice seedlings and the values of above traits in mutant bcat41 were significantly lower than those in NIP. (3) The contents of malondialdehyde and hydrogen peroxide, and relative conductance increased with the increase of treatment days in the leaves of both rice seedlings and were significantly higher in bcat41 than in NIP. (4) The differences of the morphological, growth and physiological traits between the two rices in roots were less than those in leaves. It was found that BCAT4 mutation aggravated the decrease of chlorophyll content in rice seedling leaves, inhibited the accumulation of osmotic substances and the increase of antioxidant enzyme activities in the shoots, and promoted the accumulation of malondialdehyde and hydrogen peroxide and the increase of relative conductivity under drought stress, which resulting in reduced tolerance of rice seedlings to drought.