The effect of solvents on the liquid-phase cracking of thermosetting resins was examined in the presence of tetralin (hydrogen-donor solvent), decalin (nondonor solvent), or petroleum heavy oil with a reaction time of 60 min at 430-450 degrees C in a 200-mL autoclave under 2 MPa of initial nitrogen atmosphere. Epoxy and novolak-type phenol resins, as typical thermosetting resins, showed almost 100 wt % conversion and about an 85 wt % yield of distillable oil when an iron oxide-sulfur catalyst and tetralin solvent were used. With decalin, the oil yield from epoxy resin decreased to 75 wt %; however, the phenol resin gave an extremely low conversion of 30 wt % with an oil yield of 25 wt %. Cracking of a resol-type phenol resin gave only 9 wt % conversion with decalin but increased to 99 wt % with tetralin. ABS and urethane resin also showed high conversions of more than 90 wt % and oil yields of 60-90 wt % with tetralin. In all experimental runs, gas yields were very low at 1-3 wt %, except for the case of urethane foam in which about 20 wt % of carbon dioxide was produced. In the oil produced from epoxy and phenol resins, 40-74 wt % of phenol compounds were detected. This indicates that liquid-phase cracking proceeds through simple bond dissociation followed by quick hydrogen supply from tetralin without any condensation.