In this paper, the problem of channel estimation for Superposition Coded Modulation-Orthogonal Frequency Division Multiplexing (SCM-OFDM) systems over frequency selective channels is investigated. Assuming that the path delays are known, a new channel estimator based on modified Kalman filter algorithms is introduced for the estimation of the multipath Rayleigh channel Complex Gains (CG). In the simulation, the Mean Square Error (MSE) and Bit-Error-Rate (BER) performances are given to verify the effectiveness of the Kalman estimation algorithms for SCM-OFDM systems.