This study examines the relationship between market uncertainty and tax avoidance. We can make two distinct predictions on how uncertainty affects tax avoidance. On the one hand, uncertainty increases the precautionary motive of holding cash, and managers may increase the level of tax avoidance as a way of reducing cash outflow. On the other hand, uncertainty increases the value of waiting to invest and from the point of view that tax avoidance strategy is one of many alternative investment strategies, managers may decrease the level of tax avoidance under uncertainty. We empirically examine how uncertainty affects tax avoidance and further examine firm value implications of tax avoidance. Using 9,687 firmyear observations for the period from 2005 to 2020, we provide evidence that managers reduce the risky and aggressive forms of tax avoidance under uncertainty, and that the negative effect of aggressive tax planning on firm value is mitigated.