This study examines the effect of KCl on the slow pyrolysis of lignin. Commercial alkali lignin was chosen as reference compound and it was demineralized through a washing procedure using two different leaching media, distilled water and a HF water solution at 3 wt.%. The ICP/MS analyses of the demineralized samples showed that the HF washing procedure was more effective than the water washing in reducing the K ions contents of the raw lignin. The HF demineralized sample was doped with an amount of KCl corresponding to 0.6 wt.% of K ion using the wet impregnation procedure. Subsequently, thermogravimetric (TG) analysis and slow pyrolysis tests of raw, demineralized and doped lignin samples were performed at a heating rate of 5 °C/min up to 900 °C and 700 °C, respectively. Gas species release was monitored along the pyrolysis temperature. The reduction of K ions slightly affected the pyrolytic behaviour of the raw sample by delaying both the onset of the lignin decomposition reactions and the maximum weight loss rate by about 10 °C. Moreover, the reduction of the alkali metals content enhanced the weight loss in the range of 330 and 450 ºC, thus affecting only negligibly the solid residue yields at 700 °C. Finally, it was observed that the KCl addition promotes decarboxylation reactions and dehydrogenation of the char matrix and depresses the carbon monoxide production.