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Over the past millennium, there have been several precipitation temperature cycles characterized by instabilities in the eastern monsoon region in China, but the processes, factors, and anthropogenic activities potentially responsible remain poorly understood. In this study, we present an analysis of phytoliths from borehole core drilled through an ombrotrophic peat mire in Jiangxi Province, China. Our results record three climatic episodes over the past 1300 year: a warmer interval, c. 800-1305 CE, similar to the Medieval Warm Period (MWP); a cooler interval, c. 1305-1860 CE, similar to the Little Ice Age (LIA); and another warmer interval, as the climate entered the Present Warm Period (PWP) after c. 1860 CE. Quantitative analysis of phytolith assemblages demonstrates that the MWP comprised two intervals: the early MWP, c. 800-1140 CE, was progressively wetter in a warm dry setting and late MWP, c. 1140-1305 CE, was warm and humid. The LIA also comprised two intervals: the early LIA, c. 1305-1610 CE, was cool and dry, and the late LIA, c. 1610-1860 CE was cool and humid. Some abrupt climate events occurred at: (1) c. 1050, 1110-1130, and 1780-1845 CE (wet events); (2) c. 1980-1990 CE (dry events); (3) c. 920 and 1770 CE (warm events); (4) c. 980 and 1050 CE (cold events). The transition from the MWP to the LIA, as indicated by phytoliths, was a gradual process that took c. 100 years, and exhibited frequent temperature fluctuations. Correlations between the phytolith assemblages and the solar activity, East Asia Summer Monsoon, El Nino, and La Nina are evident. Solar maxima and La Nina-like conditions are related to warmer and humid conditions that led to clay sand accumulation during the MWP. Solar minima and El Nino-like conditions were associated with a cold and wet climate that led to peat accumulation during the LIA. These observations provide important insights into paleoclimatic change in the eastern monsoonal region of China, and provide a basis on which to understand the response of the Xishan Mountains in SE China to the MWP and LIA, and explore centennial-scale climate fluctuations and their driving mechanisms.