The mangrove ecosystem significantly contributes to nutrient and carbon exchange. It is primarily stored in the soil as organic matter, significantly benefiting the surrounding organisms. However, it could be changed depending on its surrounding conditions. This research aimed to determine the percentage of soil carbon-nitrogen and its ratio in two mangrove ecosystems, one with high anthropogenic impact (TAHURA Ngurah Rai) and the other on a small island (Lembongan Island). We collect soil samples on 14 plots at each station at 0-30 cm depth and use carbon titration and TN-Kjeldahl methods for soil carbon-nitrogen measurement. The result shows substantial disparities in soil carbon levels between these ecosystems, but the soil nitrogen content was comparable. Two specific plots at TAHURA Ngurah Rai (T8 and T11) were found at low soil carbon levels due to the damage to the mangrove forest. The C/N values vary between stations, primarily because of their different sources (TAHURA Ngurah Rai: human activities, Lembongan: marine organisms). The C/N value at TAHURA Ngurah Rai is higher than the Redfield ratios, while Lembongan Island is on the contrary. However, its levels at both stations are still categorized as common conditions for mangrove ecosystems compared to various sites in Indonesia. Future research will involve measuring radioisotope characteristics to verify the origin of nutrients in these ecosystems. Obtaining measurements of environmental parameters is also necessary to provide a more comprehensive explanation of the results.