The effects of zeolite catalysts and reaction conditions on the ring-shift isomerization of sym-OHP into sym-OHA were studied through experiments at 200-300 degrees C under an initial pressure of 0.79 MPa N-2 or H-2. Eight catalysts were examined, including three hydrogen mordenites, two noble metal loaded mordenites, and three Y-zeolites. Among the three mordenites, the catalyst with lower acidity (HML8) displayed the best selectivity to sym-OHA but the lowest activity. Among the three Y-zeolites, best selectivity to sym-OHA was achieved with NiHY, which has lower acidity and lower content of stronger acid sites. The activity for syn-OHP conversion is : Pd/HM30A > Pt/HM30A > HY approximate to LaHY > HM20A > HM30A > HML8 > NiHY. The selectivity to sym-OHA decreases almost linearly with increasing conversion beyond the pseudo-equilibrium stage (about 50% conversion). The desirable condition over HML8 is 250 degrees C for 0.5 h. The other catalysts with higher acidity (HM20A, HM30A, and HY) are promising catalysts at 200 degrees C. Molecular mechanics calculations were performed to establish the upper limit of the catalytic conversion. The calculations and experimental results indicate that reaction temperature has a moderate effect on the equilibrium yield of sym-OHA, whose formation is favored at lower temperature. However, the experimentally determined equilibrium ratios of sym-OHA to sym-OHP (close to 1.3) are lower than the calculated values (2-2.6). The occurrence of simultaneous side reactions probably contributes to the shift of the equilibrium state of sym-OHA and sym-OHP.