Limonite is one of the nickel lateritic ores that has an abundant amount in Indonesia. Not only nickel, limonite ore also contains many dominating compounds, such as hematite (Fe2O3), silica (SiO2), and alumina (Al2O3). Those compounds can complicate the process to increase nickel content in the limonite ore. One of the options to reduce other compounds that act as impurities in increasing nickel is using additive in pyrometallurgical/roasting process of limonite ore. Additive used in this study is Na2CO3, with the Na2CO3: limonite ore ratio varied as 0:4; 2:4; 3:4; and 4:4. The temperature of the process was approximately 825°C, determined with STA (Simultaneous Thermal Analysis) method, while characterization of the samples after process was done with XRF method. The study showed that more Na2CO3 added resulted in less content of Fe2O3, SiO2, and Al2O3 in the ore after roasting, supported with XRF data of the samples. This was possible because they reacted and binded to Na2CO3 and formed new phase, such as Na2SiO3 and Na2MgSiO4. However, Na2O shows different result from the other compound, it was increasing with the more addition of Na2CO3. It was because additive Na2CO3 increase sodium content in the ore and the reactions between Na2CO3 and other compounds in the ore created more Na2O.