As part of the environment-related stimulus package implemented in the aftermath of the 2008 global financial crisis, the Japanese government introduced tonnage and acquisition tax breaks as well as a subsidy programme for eco-friendly vehicles. However, there has been limited research on their economic effects. Therefore, this paper employs the event study methodology to examine not only the direct economic effects of the eco-friendly vehicle tax breaks and subsidy programme on automobile firms' performance but also their spillover economic effects on automobile parts firms' performance. Our results show that the eco-friendly vehicle tax breaks had lower positive economic direct effects and no positive spillover effects while the eco-friendly vehicle subsidy programme had more significant positive direct economic effects and positive spillover effects. The differences in economic effects between tax breaks and subsidy programme result from the differences in the implementation duration and from the differences in the preferential monetary benefits. In addition, a mixed policy that combines the eco-friendly vehicle tax breaks and the eco-friendly vehicle subsidy programme is preferable to implementing the former alone.