During the growing seasons of 2006–2008, feeding tests and field studies were conducted in Beijing, China, to investigate the effects of transgenic Bacillus thuringiensis (Bt) poplar (BGA-5) expressing the Cry3A protein (0.0264–0.0326% of the total soluble protein) on target and non-target pests and the arthropod community. The effects of BGA-5 on the target pest Plagiodera versicolora (Coleoptera, Chrysomelidae) and a non-target pest Clostera anachoreta (Lepidoptera, Notodontidae), were assessed under laboratory conditions. Total mortality of P. versicolora larvae fed with BGA-5 leaves was significantly higher than that of the control (P &lt; 0.05). The exuviation index of P. versicolora larvae fed with BGA-5 tended to be higher than that of CK, but it was not significantly different. The pupation rate and eclosion rate of the survived larvae fed with BGA-5 were lower than that of CK, but it was also not significantly different. Additionally, no significant differences were detected in the mortality, exuviations index, pupation rate, or eclosion rate of C. anachoreta fed with leaves of transgenic and non-transgenic poplars. Furthermore, the arthropod communities in the Bt poplar and CK field stands were similar, as indicated by four diversity indices (Berge-Parker index, Shannon-Wiener indices, evenness index, and Simpson’s inverted index) and the Bray-Curtis index. Therefore, the Bt-Cry3A poplar decreased damage by the target pest (P. versicolora), had no effects on a non-target pest (C. anachoreta), and generally did not have any significant negative effect on the poplar arthropod community.