Abstract. Financial and non-financial disclosure play a central role in the functioning of capital markets. In this context, the Internet has been adopted as an effective mechanism for large companies to disseminate corporate information. The institutional theory approach has been applied to identify both formal (fundamentally legal and economic) and informal factors that significantly influence listed companies' level of corporate transparency on the Internet. Our work aims to build on existing study by focusing on two main objectives. Firstly, to make a comparative study of the corporate transparency of listed companies from Mexico and Spain by creating an index of corporate transparency on the Internet (e-CTI). And secondly, to identify the factors that affect this index using multiple regression analysis. Our study population is comprised of 70 companies, of which 35 belong to the Mexican Price and Quotations Index (IPyC) and 35 to the Spanish IBEX 35 index. The descriptive analysis reveals significant differences in the level of information disclosure between the two countries. The companies listed in Mexico obtain an e-CTI of 59%, while the Spanish ones register 80%, i.e. more importance is assigned to the disclosure of corporate governance data in Spain than in Mexico. Furthermore, this analysis shows that the factors most telling with regards to corporate transparency are the strength and application of law, GDP per capita, inflation and firm-level variables such as ownership concentration and Chairman of the Board-Chief Executive Officer (COB-CEO) duality. However, other variables such as board size and composition, profitability, leverage and firm size are not significant for the purposes of this analysis. Our work is of great relevance today, since most studies have focused on developed countries, mainly in the U.S. and Europe, with few comparisons being made between developed and developing countries, such as Spain and Mexico.