Modification of polymeric materials is intended to give the products specific properties or in the case of hard-to-recycle materials, facilitate their processing. In the case of biopolymers used in medical application modifiers must meet additional requirements for biocompatibility and biostability. It is important specially during modification with porous and microporous blowing agents (porophors). Their main ingredient is gas, which, under appropriate conditions of the process, expands, resulting in porosity. The use of chemical blowing agents caused among others, lower weight, enhanced damping properties, and lower processing shrinkage. The porosity constituting the gaseous phase in a cellular material, determine also the density decrease value of the product. Article presents research of modification of PLA with blowing agents in the form of polymeric microspheres. The modification was done by cellular twin-screw extrusion process. The composition include changed amount of microspheres: 0.5%, 1.5% and 3% wt. In the framework of research program differential scanning calorimetry analysis, Vicat softening temperature, thermal degradation and morphology was done. Obtained results shows that dosing microspheres have the influence on thermal properties and structure morphology.