Based on the critical solution temperature of nonionic tensioactive phosphine ligand, a novel process termed as thermoregulated phase-separable catalysis has been applied for the first time in the hydroformylation of cyclohexene. The catalyst is formed in situ from P[p-C6H4O(CH2CH2O)(n)H](3) (PETPP) and RhCl3.3H(2)O. Under the conditions of T = 130 degreesC, P = 5.0 Mpa, the conversion of cyclohexene and yield of aldehyde are 98.4%. The catalyst was reused four times and no loss in activity has been observed.