Abstract Over the past decade (2011-2021), income inequality in NTB Province has tended to increase in urban areas and decrease in rural areas. The measure commonly used to see income inequality in urban and rural areas is the Gini Ratio. Measuring income inequality using the Gini Ratio has a weakness, namely that it can only measure income inequality in one area, namely urban and rural areas; and cannot measure income inequality between regions. This study aims to determine and analyze the characteristics of income inequality within regions (within-region-inequality) on Sumbawa Island and Lombok Island, the characteristics of income inequality between regions (between-region-inequality) on Sumbawa Island and Lombok Island, and the characteristics of total or overall inequality (spatial inequality) in NTB Province. The data collection methods used in this study are questionnaire, documentation, and observation. The units of analysis are districts, islands, and the province. Data analysis was carried out using the Theil Index. The results of the analysis show that income inequality in regions/islands(within-region-inequality) on Sumbawa Island and Lombok Island, NTB Province has a decreasing trend. Meanwhile, income inequality between regions (between-region-inequality) on Sumbawa Island and Lombok Island has an increasing trend. Overall, income inequality in NTB Province has a decreasing trend during the period from 2010 to 2021. Overall income inequality in NTB Province is mostly or an average of 94.77% contributed by income inequality within regions (within-region-inequality), and only 5.23% contributed by income inequality between regions (between-region-inequality) during the period from 2010 to 2021. Key Words: Between-region-inequality, Theil Index, Spatial inequality, within-region- inequality.