The sycamore lace bug, Corythucha ciliata, is a newly found invasive insect in China. To examine the effects of piercing-sucking by C. ciliata on its host plants, we measured several physiological and biochemical traits of the London plane tree (Platanus×acerifolia) leaves injured by the bug using photosynthetic apparatus and colorimetric analysis. The results showed that with increasing leaf injury by the bug, the photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) in P.×acerifolia generally decreased. Positive relation existed between leaf injury and intercellular CO₂ concentration (Ci) (P< 0.01). After the leaf tissue of P.×acerifolia was pierced and sucked by C. ciliata adults, the chlorophyll a, b and carotenoid contents decreased compared with those of the control. There was a negative relation between leaf injury and chloroplast pigment content (P< 0.01). With increasing leaf injury, soluble sugar content decreased, but no consistent pattern of free proline content in leaves was observed. The results suggest that photosynthesis is weakened and some other physiological and biochemical parameters are changed in P.×acerifolia leaves injured by C. ciliata.