Mongolia is a sparsely populated Asian country covered by vast steppes, deserts, and forests. Few studies have been conducted on Online Citizen Science (OCS) activities in Mongolia. This study aims to analyze the state of OCS in Mongolia and, in a further step, to place it in an international context by comparing it with Germany and Japan, where OCS is already well established. Mongolia faces several environmental challenges, including climate change, land-use change, and intensive urbanization. OCS can help address these environmental challenges. Quantitative, qualitative, and literature-based analyses were conducted in this study. OCS has become more relevant in Mongolia since 2013, where projects have been introduced internationally rather than locally. A comparison with Germany and Japan showed that the use of web technologies and the degree of citizen participation in OCS projects are similar in these countries; however, the link to the United Nations Sustainable Development Goals (UN SDGs) may differ. To better respond to citizen needs and environmental challenges, additional local projects must be developed. Mongolia has the potential to enhance environmental monitoring and the networking of various actors using web technologies in citizen science.