This study aims to examine the difference of environmental disclosures between the Indonesian and Thailand mining companies, also to examine the effects of the characteristics of the companies and ISO 14001 towards environmental disclosures. This study uses firm size, firm age and profitability for the companies' characteristics. The companies' environmental disclosures were measured with the newest GRI G4 index. This study also uses the mining companies' annual reports in 2014-2016 that are listed in the Indonesia Stock Exchange (IDX) and the Stock Exchange of Thailand (SET) as the secondary data population. Furthermore, the number of samples in this research are 117 samples from 22 mining companies in Indonesia and 17 mining companies in Thailand that were generated by using purposive sampling method. The first objective has been examined by using Independent Samples T Test and it obtained a result that there are differences of environmental disclosure between Indonesia and Thailand mining companies. Meanwhile, the second and third objectives of this research were examined by using multiple regression analysis. The result shows that there are significant positive effects given by the firm size, the firm age and ISO 14001. Moreover, the profitability gives no significant positive effect towards environmental disclosures.