The consequences of tetramethylpolycarbonate (TMPC) photoageing (λ > 300 nm) on the surface modifications of the material have been analysed. Roughness and stiffness measurements were performed using AFM (Atomic Force Microscopy). Gel fraction measurements, DMTA (Dynamic Mechanical Thermal Analysis) measurements and infrared analyses were also performed. The results indicate that the three-dimensional network forms as a result of crosslinking reactions. The modifications of the properties measured using each technique were followed as functions of the irradiation time, and the influence of oxygen was characterised. The surface modifications are explained in light of the modifications of the chemical structure. Quantitative correlations were obtained between the main relevant criteria characterizing the surface degradation from the chemical structure to the mechanical properties.