The purpose of this study a relationship between goodwill and operating performance of the listed firms in the Stock Exchange of Thailand during the 3-year period of 2013 – 2015. Information from a sample group of 55 listed firms, which amounts to 165 firm years observed, was collected for analyzing by means of multiple linear regression methodology to find the relationship between the beginning goodwill, the increased goodwill, and the decreased goodwill, and the performance which is measured by core revenue. The beginning goodwill and the increased goodwill are presumed to have a positive relationship with the performance while the decreased goodwill will negatively interact with such performance.