Litter decomposition plays an important role in the maintainance of forest structure and function, and therefore, its response to environmental changes is an increasing concern. Acid rain has become a serious environmental threat in southern China in recent years. However, the response of litter decomposition to acid rain in forests of this region is poorly understood. Here, response of leaf litter decomposition for two dominant trees (Castanopsis chinensis and Schima superba) to simulated acid rain (SAR) was investigated in a monsoon evergreen broad-leaved forest at the Dinghushan Nature Reserve. Litter decomposition was measured by the litter bag method following four SAR treatments (CK, the local lake water, pH 4.5; T1, water pH 4.0; T2, water pH 3.5; and T3, water pH 3.0). SAR treatments were initiated in June 2009 and were sprayed twice a month during the study period. Results indicated that soil pH values among treatments were not significantly different in June 2010 (after SAR treatments for 13 months). However, after SAR treatments for 25 months (in June 2011), the soil pH values generally decreased with the decrease of treatment pH values with mean soil pH value in the T3 treatment significantly lower than that in the CK treatment, which indicated the aggravation of soil acidification. Meanwhile, during the decomposition period of 21 months (from October 2009 to July 2011), litter decomposition of two dominant trees has been slowed down under the stress of SAR treatments with decomposition rates of 1.18, 0.93, 0.94 and 0.86 in the CK, T1, T2 and T3 treatments, respectively in Castanopsis chinensis and 1.10, 0.97, 0.88 and 0.94, respectively in Schima superba. Mass remaining of leaf litter was also depressed after exposure to SAR treatments with CK < T1 < T2 < T3 for both tree species. In addition, similar to the gradual process of soil acidification under SAR treatments, the restrained effects of SAR treatments on the leaf litter decomposition had also been strengthened over time with significant differences of the mass remaining of leaf litter among treatments mostly occurring in the later stage of the study period. And these restrained effects on leaf litter decomposition may be correlated with the decrease in soil microbial activities caused by soil acidification under SAR treatments, as we found that soil microbial biomass carbon and nitrogen generally decreased with the decrease of treatment pH values and the T3 treatment was significantly lower than that in the CK treatment. According to the results of this study, soil carbon in forests of subtropical China would accumulate as a long-term consequence of continued acid rain.