Commercial fishing is an important industry, producing waste from fishing nets on a large scale (eg. Fishing nets, tackles). Waste fishing nets (WFN) and fishing tackles are a major source of water pollution that poses serious environmental problems, therefore they must be properly utilized. It is known that fishing nets and tackles are produced using different polymers: polyamide (nylon6), polyethylene (PE), polypropylene (PP) and polyester (polyethylene terephthalate PET). Polymers are exposed to mechanical stress, oxygen, salt water, ultraviolet radiation, therefore their polymeric chains decompose and are eroded releasing various chemical species (for example, chlorine). For these reasons, mechanical properties of fishing nets are modified, the degree of polymerisation changes, rendering fishing nets inoperable, and presence of other components can interfere with the recycling process of the substances. Thermogravimetric analysis of polymers was performed on an NETZSCH STA 449 F3 Jupiter analyser and gas evolution analysis was carried out by infrared spectroscopy during the pyrolysis and combustion. The aim of this work was to investigate the thermal changes, melting point, thermal stability, decomposition rate, dehydration, carbon and ash contents. Analysis of combustion of waste fishing nets showed the formation of chlorine and chlorinated carbon compounds. Also, thermal analysis was performed with gas evolution analysis (FTIR 3D) and chromatograms and 3D FTIR infrared spectra were obtained, representing changes in the polymer structure and composition compared to fresh fishing nets.