Photofragment yield spectra of the 3d pi L' (1) Pi(upsilon = 1) and 4p pi L' (1) Pi(upsilon = 0) Rydberg states have been observed by monitoring the fragment atoms generated by the predissociation. The Rydberg states of CO were prepared by two-color double resonant excitation through the 3s sigma B-1 Sigma(+) state, and both C(P-3 and D-1) and O(P-3) atom fragments were observed by two-photon resonant three photon (2 + 1) ionization. In particular, it has been found that the C(D-1) fragmentation takes place in these Rydberg states, which is the first evidence of the predissociation to the triplet channel. Predissociation rates to the triplet channel were estimated, indicating that the rates are comparable to those to the singlet channel.