Tax avoidance is a matter of worldwide concern, since it produces effects that impinge the proper functioning of any tax system. One of the strategies for fighting against tax avoidance is the establishment of an general anti-avoidance general rule (GAAR). This work is aimed at comparatively analyzing the procedural aspects of the Chilean GAAR and the Spanish GAAR, based on the similarities between their regulations, in order to benefit from the experience of the Spanish legislation, with achievements and shortcomings, for the complex legal activity that will entail the application of the GAAR in Chile.