Corporate social responsibility (CSR) has been widely studied in western countries in the past decades. However, the development of CSR reporting in China is at a preliminary stage. The purpose of this comparative study is an attempt to assess the quality of CSR reports of BHP Billiton and China Shenhua Energy from western world and China respectively. Being a controversial industry, companies in mining industry turn to use corporate social responsibility (CSR) disclosures as a technique to obtain legitimacy. This study also aims to explain the motivations behind these two mining companies’ CSR reporting from the perspective of legitimacy theory. The study uses content analysis to evaluate six CSR reports of two mining companies by examining the extent of corporate adoption of GRI-G3 Guidelines and measuring qualitative differences in content disclosures over the period 2011-2013. This study shows that legitimacy theory explains the reason why these two mining companies are willing to disclose CSR information voluntarily. In addition, both companies prepared their CSR reports in accordance with GRI Sustainability Reporting Guideline, but the level and content of CSR disclosures are different. This study reveals that the CSR report of BHP Billiton is of higher quality. BHP Billiton can be considered as a mature reporter while China Shenhua Energy, a growing up reporter, shows a gradual progression in the CSR reporting in the past several years.