本研究探討企業避稅行為對信用評等之影響，並將企業避稅拆分為正常避稅與異常避稅後，再分別討論企業在採行不同避稅策略下，信用評等機構是否會給予不一樣信用評等。依過去文獻預期企業從事適度避稅可以增加稅後現金流量，提高股東利益；然而企業避稅若異常激進，會惡化代理問題與稅務風險等成本增加，倘若企業避稅異常保守，則無法保留足夠現金流量，反映管理者怠惰或能力不佳等問題，是以企業從事異常激進或保守避稅皆會損害公司價值。本文以美國1989年至2014年的上市公司為樣本，實證發現信用評等機構對企業的正常避稅行為給予正面評價，對於異常避稅行為，包含異常激進與異常保守之避稅行為，皆給予負面看法。此結果顛覆了Ayers et al. （2010）指出信用評等與企業避稅之間為單調遞減關係的論述。

This study explores the impact of corporate tax avoidance on credit rating. After splitting enterprise tax avoidance into normal tax avoidance and abnormal tax avoidance, it will discuss whether the credit rating agency will give different credit ratings under the adoption of different tax avoidance strategies. According to the prior literature, it is expected that firms engaged in moderate tax avoidance can increase after-tax cash flow and improve the interests of shareholders. However, if enterprise tax avoidance is extremely radical, it will worsen the cost of agency problems and tax risks. If enterprise tax avoidance is abnormally conservative, firms cannot retain enough cash flow, reflecting problems such as managers’ laziness or poor ability. Thus, firms engaged in abnormally radical or conservative tax avoidance will harm the value of the company. This article takes public companies from 1989 to 2014 in the U.S. as a sample. It is empirically found that credit evaluation institutions give positive comments on the normal tax avoidance of firms, and give negative views on abnormal tax avoidance, including abnormally radical and conservative tax avoidance. This result subverted Ayers et al. who pointed out that the relationship between credit rating and enterprise tax avoidance is monotonous and decreasing.

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