The saturated 4.3-mu-m fluorescence frequency stabilization method has been extended to a sequence-band CO2 laser. Owing to little photon trapping, we can detect the 4.3-mu-m fluorescence with a good signal-to-noise ratio by using a longitudinal CO2 absorption cell heated to 200-degrees-C. The frequency stability estimated from the residual error signal is better than 50 kHz.