This book analyzes long-term expenditure of 4 social insurances and suggests policy reforms for financial sustainability. Specifically we covers national pension, health insurance, unemployment insurance, work injury insurance. Under certain macroeconomic assumptions, national pension system shows slightly improved financial situation, However, the reasons are unclear whether inclusion of new 3 year data or model difference play a significant role. We suggest that development of comparable models is important to improve or evaluate current very large and detailed government model. Future medical expenditure projections show similar numbers with previous researches and large fluctuations with the change of income elasticity. To improve long-term fiscal soundness, we need to adopt aggressive cost control measures and then to widen health insurance premium base and to consider increase of contribution ratio. Future expenditure level of unemployment insurance and work injury insurance are not significant compared to health insurance or national pension. Unfortunately, reserve fund of unemployment insurance will deplete in 2012, 2013 according to operation accounts because of expenditure surge. We propose more tight benefit control and contribution increase. Work injury insurance is expected to show smaller budget size than previous projections since the work injury rate has dropped significantly recently. Work injury and unemployment insurance provide very limited financial information compared with national pension or health insurance. We strongly recommend more transparent financial operation of the insurances.