The transgenic rice line T1C-19 provides high resistance to lepidopteran pests because of the synthesis of the Bacillus thuringiensis(Bt) insecticidal protein Cry1C. It thus shows good prospect for commercial planting in China. Species of Cladocera, an order of aquatic arthropods commonly found in aquatic ecosystems such as ricepaddies, might be exposed to the insecticidal protein released from Bt-transgenic rice-straw residues. For the study reported herein, we used Daphnia magna(water flea) as a representative of Cladocera to evaluate whetheraquatic arthropods are adversely affected when exposed to Bt rice-straw leachates. We exposed D. magnato M4 medium containing various volume percentages of medium that had been incubated with T1C-19 rice straw orrice straw from its non-transformed near-isoline Minghui 63 (MH63) for 21 days. Compared with pure M4medium (control), the fitness and developmental and reproduction parameters of D. magnadecreased sig-nificantly when exposed to rice-straw leachates; conversely, no significant differences between the T1C-19 and MH63 rice-straw leachate treatments were observed, indicating that the Bt rice straw leachate did not adverselyaffect this non-target species.