This study evaluates the performance of the recently released 20th Century Reanalysis (20CR) data in describing East Asian summer monsoon (EASM) variability by contrasting the results with NCEP1 and ERA40 reanalysis and instrumental datasets. This analysis focuses on the climatology, interannual variability, and decadal change of the EASM. The results show that the 20CR reanalysis data reasonably depicts the high- and low-level circulation fields, including the South Asian high, subtropical jet, and near surface wind, and the meridional monsoon circulation cell. However, in comparison with NCEP1 and ERA40, 20CR data shows a stronger South Asian high, more northward displacement of the subtropical jet, and systematically warmer air temperature in the mid- and high-troposphere. The three reanalysis datasets are highly consistent in measuring EASM variability with the exception of the period before 1967, during which interannual variability results differ due to biases in NCEP1. The monsoon indices based on zonal wind shows better consistency than those based on meridional wind, and the monsoon index based on low-level zonal wind shows the best consistency among the three datasets. 20CR reasonably reproduces interannual variability of the surface air temperature and precipitation related to the EASM, which has a westward and strongest positive correlation center and a weak negative correlation center near Hetao Plain. In addition, precipitation in the Bay of Bengal and along the Yangtze River valley is represented more accurately in the 20CR dataset than that in the other two reanalysis datasets; however, results are opposite in the tropical regions and the oceans. At the interdecadal time scale, however, the 20CR reanalysis data failed to reproduce decadal weakening of the EASM circulation, which is also reflected in its failure to reproduce the observed southern China flood and northern China draught rainfall pattern and surface cooling trend downstream of the Tibetan Plateau. These results are mainly attributed to the deficiency of 20CR reanalysis data in measuring the upper tropospheric cooling tendency over East Asia. During the past 100 years, 20CR has shown consistency in EASM changes with that of observation; this dataset has reasonably depicted the notable cold period before the 1920s and the rapid warming period after the 1990s but has shown weaker skills in presenting the relatively warm period during the 1920s-1950s and the relative cold period during the 1950s-1980s in the EASM region.