To provide a method for cracking hydrocarbon oils such as a heavy thermal decomposition oil difficult to lighten, a catalytically cracked light oil, a desulfurized decanted oil and an extract without generating cokes.

The method for cracking a hydrocarbon oil comprises cracking at least one hydrocarbon oil selected from a heavy thermal decomposition oil, a catalytically cracked light oil, a desulfurized decanted oil and an extract, in the presence of water and a catalyst containing 70 wt.% or more of a group 4A element as the oxide and containing at least one oxide selected from aluminum oxide, cerium oxide, phosphorus oxide and yttrium oxide, under the condition that a molar ratio of the above hydrocarbon oil to water (raw material hydrocarbon oil/water) is 0.01-100, at a temperature of 280-580C, and pressure of 22.1-50.0 MPa.