The transgenic Bacillus thuringiensis (Bt) rice, Oryza sativa L., lines T_2A-1 and T1c-19 expressing Cry2A^* and Cry1C^* from ‘Minhui 63’ (MH63) were evaluated for resistance to newly hatched and third-instar larvae of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), by using detached leaf laboratory bioassays. Both T_2A-1 and T1c-19 rice showed high C. medinalis resistance; however, the lethal time (LT)₅₀ of larvae fed with T_2A-1 rice was significantly longer than that of larvae fed with T1c-19 rice, implying T1c-19 rice was more toxic to C. medinalis larvae. Larval mortality after 4 d on nitrogen-free MH63 was 25.5% compared with 2.4% mortality on high nitrogen fertilizer (250 kg N/ha) plants. Larval mortality on high nitrogen T_2A-1 plants declined by 20% compared with nitrogen-free plants. However, resistance in T1c-19 plants was unaffected by nitrogen fertilizer. C. medinalis moths preferred MH63 at both the seedling and grain milk stages for oviposition but not the T1c-19 and T_2A-1 Bt rice lines.