The problem of synthesizing an optimal filter of a useful signal in a bispectral domain by the least mean absolute third error criteria is solved in the work. Core advantage of the filter is its capability to select the useful signal bispectrum theoretically ideally. At the same time the Wiener's optimum filter selects the desired signal bispectrum without an error in bispectral domain if a signal and disturbance bispectrums are not spanned. In this case the least mean square error is considerably lower after an optimal filtration by the least mean absolute third error criteria using recovering a desired signal from the bispectrum, than using Wiener’s filtration.