The objective of the study was to characterise co-composting dynamics and maturity of the end products of sewage sludge/ green waste mixtures. We analysed all initial substrates and co-composts, sampled at diferent composting times for studying (1) physicochemical parameters and (2) organic matter biodegradation and biotransformation using pyrolysis coupled to gas chromatography and mass spectrometry. Physicochemical analysis indicated compost maturity of the three co-composting mixtures after 200 days. Pyrolysis-GCMS showed that organic matter in sewage sludge generated a large number of diferent pyrolysis products, most of which had unspecifc origin. The pyrolysis products of the three co-compost were classifed according to their chemical composition (benzene derivatives, N-containing compounds, phenol derivatives, furan derivates) and according to their chemical structure (polyaromatics, aromatics compounds and aliphatic compounds). These compound classes evolved diferently during composting. We suggest two new specifc ratios of peak areas from pyrolysis products to describe the biodegradation and to evaluate the degree of maturity during co-composting sludge-green waste: (1) the ratio benzene, methyl (methylethenyl) /benzene, which decrease during composting, and (2) the ratio of Indene/2-methoxy-4 vinyl-phenol which increase during composting. The good correlation between these ratios and physico-chemical parameters confrms their usefulness to evaluate the co-compost maturity.