Effects of mineral-based fire retardants were investigated relative to the thermal and fire properties of medium-density fiberboard (MDF) via thermogravimetric analysis (TGA), limiting oxygen index (LOI), and thermal conductivity testing. Mineral-based chemicals containing huntite/hydromagnesite and zinc borate (ZB) were used at different concentrations. Changes in all values were observed depending on the type and concentration of chemicals. According to TGA evaluation, the residual weights in the MDF samples manufactured with mineral-based chemicals were higher than the residual weight in the control MDF sample. Limiting oxygen index testing results showed higher values for the MDF samples manufactured with mineral-based chemicals than for the control sample. The LOI values increased with the increment of chemical concentration, and the highest value was observed in group B12. The thermal conductivity trends of the MDF samples varied depending on the type and concentration of chemicals. Generally, the thermal conductivity values of the MDF samples manufactured with chemicals were found to be higher than the value of the control. These results suggested that these chemicals with various combinations should be evaluated as fire retardants for wood and wood-based panel industry.