“The Social Return on Investment Projects (SROI) under the Implementation of the District Health Board (DHB): 4 Case Studies” aimed to analyze social return on investment (SROI) of district health board and to assess the implementation of district health quality development under the drive of 4 DHBs in order to synthesize policy recommendations for the short, intermediate, and long terms of district health quality development through all concerned stakeholders’ engagement. There are 4 projects in the 4 targeted areas, as follows: 1) Elderly care in Bang Kruai DHB, Nonthaburi Province; 2) Waste and environmental management in Phimai DHB, Nakhon Ratchasima Province; 3) Traffic Accident reduction of in Suk Samran DHB, Ranong Province, and; 4) Good agriculture and safe food in Laplae DHB, Uttaradit Province. Mixed methodology was implemented based on the concept of social return on investment (SROI), under the guideline on the implementation of district health board (DHB), through documentary research from secondary data, survey questionnaire, focus group, and in-depth Interviews as data collection process. The results of social value or and the change in the community was transformed into financial proxy by net present value (NPV) analysis, 6% and 3% discount rates, cost-benefit analysis, payback period, and the ratio of SROI. Inputs, activities, outputs and outcomes were also analysed in the establishment of mapping outcome process. The conclusions from the focus group were made into impacts that required deadweight analysis by focusing on the weights of changing activities and other supporting factors that affected attributions. Then, financial proxies of the projects were calculated under the guideline on district health board (DHB). The results of SROI study from the project implementation in 5, 10, and 15 years with the use of discount rate at 6 and 3 percent were revealed as follows. 1) The elderly care project of Bang Kruai DHB, the SROI with 6% discount rate used of this project is -0.18 (in 5 years), 0.15 (in 10 years), and 0.26 (in 15 years). The calculated SROI with 3% discount rate revealed -0.17 in 5 years, 0.22 in 10 years and 0.38 in 15 years. The result showed the payback period in 4.72 years (5 years), 6.43 years (10 years), and 8.73 years (15 years). These implies that the calculation of SROI with 6% and 3% of discount rate mean every 1 THB of investment in the elderly care project of Bang Kruai DHB, - 0.18 THB in 5 years, 0.15 THB in 10 years, and 0.26 THB in 15 years of social value is created when the discount rate is at 6%; however, if the 3% discount rate is used, every 1 THB of investment in the elderly care project of Bang Kruai DHB, - 0.17 THB in 5 years, 0.22 THB in 10 years, and 0.38 THB in 15 years of social value is created, respectively. 2) The waste and environmental management of Phimai DHB, the SROI with 6% discount rate used of this project is 6.80 (5 years), 6.76 (10 years), and 6.18 (15 years). The calculated SROI with 3% discount rate revealed 7.52 in 5 years, 7.98 in 10 years and 7.75 in 15 years. The result showed the payback period in 13 days for 5 years, 26 days for 10 years, and 1.28 months for 15 years. These implies that every 1 THB of investment in the waste and environmental management of Phimai DHB is able to create social values at 6.80 THB in 5 years, 6.76 THB in 10 years, and 6.18 THB in 15 years if the discount rate is at 6%, while the discount rate at 3% explores every 1 THB of investment in the waste and environmental management of Phimai DHB is able to create social values at 7.52 THB in 5 years, 7.98 THB in 10 years, and 7.75 THB in 15 years. 3) The traffic accident reduction project of Suk Samran DHB, the SROI with 6% discount rate used of this project is 13.02 (5 years), 11.38 (10 years), and 10.01 (15 years). The calculated SROI with 3% discount rate revealed 14.16 in 5 years, 13.19 in 10 years and 12.30 in 15 years. The result showed payback period in 0.30 months (5 years), 0.61 months (10 years), and 0.91 months (15 years). These implies that every 1 THB of the traffic accident reduction project of Suk Samran DHB invested, 13.02 THB in 5 years, 11.38 THB in 10 years, and 10.01 THB of social value is created when using 6% discount rate, while if discount rate is at 3%, every 1 THB of the traffic accident reduction project of Suk Samran DHB invested, 14.16 THB in 5 years, 13.19 THB in 10 years, and 12.30 THB in years of social value is created. 4) The good agriculture and safe food project of Laplae DHB, the SROI with 6% discount rate used of this project is 1.10 (in 5 years), 1.36 (in 10 years), 1.34 (in 15 years).The calculated SROI with 3% discount rate revealed 1.21 in 5 years, 1.62 in 10 years and 1.71 in 15 years. The result showed the payback period in 1.70 years (for 5 years), 2.80 years (for 10 years), and 4 years (for 15 years). These implies that every 1 THB of the good agriculture and safe food project of Laplae DHB invested, the social value at 1.10 THB in 5 years, 1.36 THB in 10 years, and 1.34 THB in 15 years is created if calculating with 6% discount rate. However, if 3% of discount rate is used, The investment of every 1 THB of the good agriculture and safe food project of Laplae DHB is likely to create the social value at 1.21 THB in 5 years, 1.62 THB in 10 years, and 1.71 THB in 15 years.