The present invention relates to a method for producing a niobium solid electrolytic capacitor using niobium as an anode body, which comprises a step of chemically converting the anode, wherein the chemical conversion step comprises a first chemical conversion step of forming a chemical conversion coating of the anode, a step of heating the anode body having been subjected to the first chemical conversion step, and a second chemical conversion step of once again chemically converting the heated anode body; wherein electrolytic chemical conversion is performed in the first chemical conversion step and the second chemical conversion step using a chemical conversion liquid, which contains a metal nitrate salt as an electrolyte, at a temperature from 40° C. to the boiling point of the solvent; and wherein the heating step is performed at a temperature of 150 to 300° C. The method for producing a niobium solid electrolytic capacitor of the present invention can increase the stability of an oxide film which functions as a dielectric body and prevent increase in leakage current, thereby improving the yield and reliability in the method for producing a niobium solid electrolytic capacitor.