The paper proposes and investigates a new type of nonlinear adaptive canceller of intersymbol interference (ISI) called ‘ACDEC’. The ACDEC uses an automatic equaliser including a decoder of an error-correcting code (AEDEC), to obtain more reliable preliminary decisions than those by the linear equaliser used in the linear adaptive canceller of Gersho and Lim. By using the modified structure and incorporating one more decoder, the tap values of both the canceller's delay line and the adaptive matched filter are correctively updated with reduced final decision errors in the same manner as AEDEC. The theoretical calculation of the error probability in the joint repetitive scheme of both cancelling ISI and decoding indicates that two repetitions, i.e. ACDEC, can provide considerable improvement in the error probability performance in the steady state without excessive complexity of implementation. Moreover, computer simulations show that an ACDEC achieves stable convergence and exhibits better adaptability in noisy and time-varient channels.