The green remediation assessment tool for Japan (GRATJ) presented in this study is a spreadsheet-based software package developed to facilitate comparisons of the environmental impacts associated with various countermeasures against contaminated soil in Japan. This tool uses a life-cycle assessment-based model to calculate inventory inputs/outputs throughout the activity life cycle during remediation. Processes of 14 remediation methods for heavy metal contamination and 12 for volatile organic compound contamination are built into the tool. This tool can evaluate 130 inventory inputs/outputs and easily integrate those inputs/outputs into 9 impact categories, 4 integrated endpoints, and 1 index. Comparative studies can be performed by entering basic data associated with a target site. The integrated results can be presented in a simpler and clearer manner than the results of an inventory analysis. As a case study, an arsenic-contaminated soil remediation site was examined using this tool. Results showed that the integrated environmental impacts were greater with onsite remediation methods than with offsite ones. Furthermore, the contributions of CO2 to global warming, SO2 to urban air pollution, and crude oil to resource consumption were greater than other inventory inputs/outputs. The GRATJ has the potential to improve green remediation and can serve as a valuable tool for decision makers and practitioners in selecting countermeasures in Japan.