The study aims to measure income disparity in ancient Japan before the onset of modern economic growth. Specifically, the analysis relies on the estimation of the institutional income of peasants and government officials under the Ritsuryō regime in Nara-period Japan. Historical documents such as ancient laws and regulations were used as sources of data. The results of the study indicate that 30%–40% of peasants’ income was collected as land tax (so), poll taxes (yō and chō), and compulsory public loans (suiko). Income was earned from the cultivated land allocated by the Ritsuryō government. In particular, the tax burden ratio of poll taxes and compulsory public loans was high. Government officials without any tax burden can be divided into the following classes according to income levels: upper nobles, middle and lower nobles, and general officials. The income level of the upper nobles was remarkably high. The results of the study indicate the prevalence of income disparity among government officials. The incomes of general officials were higher in the local branch offices than in the central government. A comparison between social classes does not confirm a large difference between peasants and the general officials. However, the finding shows an extremely high disparity in income between peasants and upper nobles. Although the result is not based on actual income but rather on institutional income, it can be said that the ancient Ritsuryō regime was established on the basis of a system that produced a very high level of income disparity.
