Selective ring opening of decalin was investigated over various metal-modified zeolites in order to shed light on the key parameters affecting the selectivity to ringopening products at low extent of cracking reactions. Ir-modified zeolites H-Y and H-Beta having different concentration and strength of acid sites were studied in a batch reactor at 250-310 °C and 20-60 bar H2 and their performance was compared with that of Pt-modified zeolites. The concentration of Brønsted acid sites, reaction temperature and hydrogen pressure were shown to be the crucial reaction parameters. To obtain high selectivity to formation of ring-opening products from decalin, mildly acidic Ir-modified Beta was the best choice when the reaction was carried out at temperature of 270 °C or lower and at H2 pressure of 60 bar. Under these conditions the selectivity and yield of ring-opening products exceeded 65 and 60%, respectively.