Abstract: Lanthanum iso-nicotinate was synthesized by using nicotinic acid, lanthanum nitrate and sodium hydroxide as raw materials, and its structure and composition were analyzed and characterized. The effect of lanthanum iso-nicotinate on the thermal stability and discoloration of poly(vinyl chloride) (PVC) was studied by means of the Congo red and high temperature aging methods. A comparative investigation on heat stability was also performed for the PVC compounds stabilized with different heat stabilizers including lanthanum stearate, zinc stearate, calcium stearate and pentaerythritol. The results indicated that lanthanum iso-nicotinate could not generate an ideal and long-term heat-stabilizing effect on PVC when used alone, and the anti-discoloration capability was also not good. The PVC compounds achieved the stability time of 22 min at a stabilizer loading of 2.5 wt% when the weight ratio of lanthanum iso-nicotinate/zinc stearate/pentaerythritol was set to 3/1/1. The stabilization mechanism of lanthanum iso-nicotinate could be attributed to the absorption of the HCl released by decomposition of PVC, resulting in the production of LaCl3. This reduced the catalytic effect of HCl on the decomposition of PVC and thus inhibited its degradation.