Correlations between the free carrier lifetime of thick, lightly-doped n-type 4H-SiC epilayers and some deep levels (the Z(1/2) center, the EH6/7 center and the D, center) were investigated. Concentrations of the Z(1/2) center and the EH6/7 center correlated with the measured carrier lifetime to some extent. We have also compared the free carrier lifetime measured by time-resolved photoluminescence (TRPL) measurement and microwave-detected photoconductive decay (mu-PCD) measurement. The carrier lifetime measured by both technique was in close agreement. The carrier lifetime measured by LTPL increased at an elevated temperature of 500 K.