This study investigates the conditions under which host country portfolios are more likely to regularize corporate tax behavior. We use a sample comprising data on Japanese multinationals covering 2004 to 2014 to examine the relationship between foreign direct investment host country portfolios and tax avoidance from the perspectives of investor protection and ethical standards. Our multivariate regression results show that the number of countries with strong investor protection/high ethical standards in the FDI host country portfolio is negatively related to tax (...) avoidance. We also find that the effect of investor protection/ethical standards is less pronounced when the degree of indulgence is high. Further analyses show that the relationships we find are affected by disclosure requirements, local regulations, and accounting standards. These findings remain unchanged after several sensitivity checks. Overall, this study contributes to the business ethics literature by showing that FDI host country investor protection and ethical standards are external monitoring mechanisms for mitigating tax avoidance by multinationals. (shrink)