Deep levels in bulk crystals of 6H- and 4H-SiC, and epilayers of 4H-SiC were studied using optical-isothermal transient spectroscopy (O-ICTS) and conventional dark ICTS methods, for the first time. For 6H-SiC bulk, E1 with 3x 10(15) cm(-3) (E-c-0.32 eV), E2 with 5x 10(14) cm(-3) (E-c - 0.49 eV) and E3 with 7x 10(14)cm(-3) (E-c- 0.50 eV) were observed by dark ICTS. Further, E4 with 1x 10(15) cm(-3), which was located between below E3 and above E-c - 1.96 eV, was observed by O-ICTS. On the other hand, for 4H-SiC bulk, one dominant deep level (E5 with 1x 10(15) cm(-3) located at E-c - 1.15 eV) and one minor lever (E6 with 3 x 10(14) cm(-3) located at deeper than E5) were observed by both dark- and O- ICTS. However, for 4H-SiC epilayer, no significant levels were observed either by dark-or O-ICTS, which is consistent with the case of 6H-SiC epilayer reported previously.