Water is one of the most essential factors for survival and growth of lichens. Their metabolisms depend on thallus water content, which rely on atmospheric humidity, rain, dew and fog. The aim of this study was to observe variations of ne tphotosynthesis (NP), efficiency of PSII (Fv/Fm, ΦPSII and ETR) and photosynthetic pigments (Chl. a, b, a+b, a/b) of lichen Parmotrema tinctorum (Despr. ex Nyl.) Hale influenced by annual rainfall at Khao Yai National Park. The study was performed during September 2010-August 2011. The results showed that all physiological parameters likewise responded to rainfall. Those values were higher during rainy period (late February-mid October) and lower during dry period (late October-mid February), particularly in late drought all parameters were extremely low. However, after rain began, the values of those parameters raised even in the hot season. In addition, statistical testing illustrated that some physiological parameters had high positive correlation with rainfall and wet days. Therefore, physiological performance of this lichen closely related with rainfall regardless of seasons. Furthermore,obvious decline of NP after exposure to long dry period indicated that carbon assimilation was the most sensitive parameter to drought. Moreover, this work also demonstrated that photosynthetic related parameters of this species distinctly showed statistical significant positive correlations among each other.