The introduction of epoxy groups on the main chain of polydiene has emerged as a fruitful route to monitor polymer-filler interactions leading to useful changes of physical properties of the vulcanisates. The in situ epoxidation reaction was chosen to modify polybutadiene and poly(butadiene-co-styrene), due to the easy control of the reaction even for small degrees of epoxidation. The extent of modification of the polymer chain was quantitatively accompanied by means of FT-IR and 1H-NMR spectroscopy. The shifts of the Tg's to higher temperatures with the increase of the epoxy content on the polymer chain was monitored using the DSC analysis. From the temperature and amplitude dependency of the dynamic moduli it can be concluded, that the interaction of the epoxidised rubber matrix with silica is greatly improved even for small contents of epoxy groups in the rubber chains.