The aim of this study is to evaluate the life-cycle environmental load of a ground source heat pump (GSHP) in Bangkok, Thailand. We conducted a life-cycle inventory analysis based on the assumption of the introduction of an optimally-designed GSHP to a commercial facility in Bangkok, Thailand. An air source heat pump (ASHP) was selected as a comparison target. Moreover, sensitivity analysis was conducted based on thermal conductivity and subsurface temperature to clarify the influence of changes in groundwater flow and subsurface temperature. Indicators of analysis were the life-cycle CO2, NOX, and SO2 (LC–CO2, LC–NOX, and LC–SO2, respectively) emissions. As a result, the LC–CO2, LC–NOX, and LC–SO2 emissions of GSHP were reduced by 27.8%, 24.8%, and 25.6%, respectively compared with ASHP. The LC–CO2 emissions of GSHP within the scope of sensitivity analysis were reduced by 26 to 28.6% compared with ASHP. These results show the GSHP in Bangkok could achieve smaller environmental load than the ASHP and the changes in groundwater flow and subsurface temperature do not greatly influence on the life-cycle environmental load. However, this study indicated that the large ground heat exchanger is required compared to the other areas, e.g., United Kingdom, and China. This means the economical and space constraints would be the barrier of introduction of GSHP in Bangkok. Therefore, further research is required to evaluate not only the environmental aspect, but also the economic aspect.