The thermal stability of blends consisting of polyethylene (PE) or isotactic polypropylene (PP) with two different semiflexible liquid crystalline polyesters (LCP) was analysed by thermogravimetry (TG) under nitrogen and air atmospheres. The effects of the structural parameters of the LCP and of its content in the blends were evaluated. The temperatures at which degradation starts indicated that the stability of the mixtures is governed by the presence of the less stable component, under the experimental conditions applied. Comparison between predicted and experimental weight losses versus temperature support speculations on polymer-polymer interactions in the blends.