Tidal lands are estimated to cover an area of 20.13 million ha, of which 17,828 ha are located in South Kalimantan. Tidal lands are indicated as a source of greenhouse gas emissions, so they need to be balanced with the return of carbon-containing materials such as biochar. This study aims to determine the effect of biochar type and size on biomass C and N-microbes in tidal lands. The study used soil taken from Tinggiran II Luar Village, Barito Kuala Regency, South Kalimantan Province. The soil was given galam wood, rambai, and rice husk biochar measuring 10 and 100 mesh at a dose of 70 g/7 kg of soil. After incubation for 3 weeks, the soil was collected and used for C and N biomass analysis. The results showed that the application of biochar to tidal land had a significant effect on pH. However, there was no significant difference in microbial C and N biomass. Treatment A1B1 showed the highest results for pH, microbial C and N biomass. These results indicate that biochar application can increase soil pH and return C and N to the soil.