Effect of Y substitution on the La-based iron oxypnictide superconductor LaFeAsO0.6 is studied. Replacement of La3+ (1.16Å) by smaller Y3+ (1.019Å) in a form of La1-xYxFeAsO0.6 results in the decrease in lattice parameters, which likely causes pressure effect into the system. Superconducting transition temperature (Tc) increases monotonically with x , eventually up to 43.1 K for x=0.5 . This Tc is comparable to the highest Tc reported for Y-free F-doped LaFeAsO1-xFx under high pressure. The present results provide an alternative and much simpler way to achieve higher Tc in the La-based oxypnictide superconductors.