To investigate the effect of acid mine drainage on organic matter processing, we measured leaf breakdown in a third-order stream in South China. We used leaves of Dracontomelon duperreanum (Anacardiaceae) and Syzygium jambos (Myrtaceae) allocated into coarse (5mm) and fine (0.1mm) mesh bags. The stream was polluted by acid mine drainage with low pH (2.7—3.4) and heavy metal-rich water drained from the Dabaoshan Mine of Guangdong, China. After 101 days in the stream, 39% (coarse-mesh bags) to 48% (fine-mesh bags) of D. duperreanum initial mass still remained in the stream, whereas for S. jambos the values were 61% (coarse-mesh bag) and 70% (fine-mesh bag). The time required for a 50% loss of leaf litter, based on the exponential model, were 57 days (coarse-mesh bag) and 69 days (fine-mesh bag) for D. duperreanum, and 144 days (coarse-mesh bag) and 217 days (fine-mesh bag) for S. jambos, respectively. The decomposition rate of D. duperreanum leaves was significantly faster than that of S. jambos. Macroinvertebrates colonizing the coarse-mesh bags consisted mainly of collector-gatherers, of which Chironomidae larvae were numerically dominant in and accounted for more than 99% of the total macroinvertebrate individuals. The number of chironomids in the bags fluctuated along time, but no relationship was observed between number of chironomids and mass losses, which suggests that the contribution of chironomids to the breakdown of leaf litter was thus unimportant. Our results suggest that the macroinvertebrate biodiversity can be seriously reduced in the stream impacted by acid mine drainage and the decomposition rate of leaf litter in the stream can be slower, mainly as a result of inhibition of microbial activity due to hypoxia with the deposition of metal oxides on leaf surface.