Drought is a major disturbance that greatly influences the structure, composition, dynamics and primary production of a forest. Since drought frequency and strength are predicted to increase in the future, understanding the response of natural forests to drought is crucial for predicting the performance of forests under global climate change. In late 2009 and early 2010, a severe drought (rainfall anomaly) occurred in Southwest (SW) China. This severe drought event had a large impact on the regional agriculture and economy of this region, and attracted great attentions of scientists and the public. It has also been recognized as the most severe drought of a century. However, the impacts of this severe rainfall anomaly on natural ecosystems were not well assessed. The objectives of our study were (1) to evaluate the impacts of this rainfall anomaly on forest canopy and litterfall of natural forests in this region, and (2) to establish the relationship between climatic factors and litterfall for natural forests in this region. In the present study, we compared the litterfall and its different components, as well as the leaf area index of different forest layers of an evergreen broadleaf forest onAilao Mountain between the 2010 unusual drought and the previous year drought with normal rainfall amounts. We also analyzed the relationship between litterfall and climatic factors, including annual mean temperature, annual rainfall, and annual number of rainy days. No significant difference was found in annual litterfall between 2010 and the previous years. However, annual leaf fall, dry season litterfall, and dry season leaf fall in 2010, were higher than those in any previous year. Dry season leaf fall in 2010 was 35.2% (0.81 t/hm²)higher than the average during normal years. Notably, the annual fall of epiphytic mosses in 2010 was a historical minimum. No difference was found in leaf area index of the overstorey and understoreylayers between 2010 dry season and 2005 dry season (a year with a normal rainfall amount).However, leaf area index of the herbaceous layer in 2010 dry season was significantly lower than that of the 2005 dry season. Therefore, although the regional rainfall anomaly in early 2010 increased leaf fall in the dry season, it did not significantly influence the canopy leaf area index. The growth of the herbaceous layer and the epiphytic mosses, howeverwere significantly affected. A significant positive relationship between annual litterfall and annual rainfall, as well as a negative relationship between dry season litterfall and dry season rainfall were found. There was no relationship between annual litterfall (or its components: leaf, stem, epiphytic mosses) and mean annual temperature. Therefore, the primary production and litterfall of this subtropical forest is determined by rainfall rather than by temperature. This pattern is different from the result from a previous study in Northeast China, showing that forest litterfall is mainly determined by mean annual temperature. This could be because subtropical forests are relatively warmer than the temperate forests in Northeast China, and temperature is not a major limiting factor on the forest primary production and litterfall of subtropical forests. This relationship could be further tested in other subtropical forests to reveal more general patterns.