Today polymers are one of the most important technical materials and serve as a substitute for the usual materials (wood and metal). Each polymer has characteristic structure and therefore different properties which affects their use. In this work thermal properties and thermal stability of polystyrene (PS), high-impact polystyrene (HIPS), low-density polyethylene (PE-LD), high-density polyethylene (PE-HD), polycaprolactone (PCL), polylactide (PLA) and polyurethane (PUR) were investigated. Characteristic value of transition temperatures and enthalpies were determined using differential scanning calorimetry (DSC). Thermal stability was determined with thermogravimetric analysis (TGA). The DSC analysis showed that amorphous polymers, PS and HIPS have high glass transition temperatures due to the benzene rings which stiffen their structure and prevent rotations of macromolecules segments. Opposite of the polystyrenes are PE-LD and PE-HD, which have a very low glass transition temperature due to the higher rotation of macromolecules segments as a consequence of their simple structure. PE-HD crystallize more, crystallization is faster and more arranged crystals are form due to less branching than in PE-LD. PLA and PCL are biodegradable and crystalline polymers, but they crystallize differently and have completely different glass transition temperatures. Crystallization of PLA is slower and it has higher glass transition temperature due to methyl groups in its main chain which limits the rotation of macromolecules segments and hinder the crystallization. Thermal properties of PUR depend on its structure, i.e. proportion of hard and soft segments. Results showed that PUR and PLA have similar characteristic transitions, but glass transition, as well as crystallization and melting temperatures of PLA are at significantly higher temperatures, compared to PUR, as a consequence of macromolecules stiffness. The results of thermal stability showed that the most stabile is PE-HD, while PE-LD is a little less stable, due to more branched structure, which limits the formation of crystalline forms with strong secondary bonds. The lowest thermal stability of all tested polymers in this work has PLA.