This paper proposes a new channel interference cancellation technique using interference estimation and double optical hardlimiters (DHLs) for direct-detection optical code-division multiple-access systems. In the proposed system, when the output of the DHL is "0", the proposed system outputs "0". When the output of the DHL is "1", the proposed system reconstructs the interference and estimates whether the output "1" is owing to the interference or the transmitted signal. It is shown that the proposed system is effective to reduce the effects of the channel interference. Moreover, it is shown that the proposed system can improve the error floor of the systems with DHL.