In psychological noise evaluation, the fuzziness caused by the human subjective judgment for the acoustical stimulus essentially exists, By paying special attention to the fuzziness of the subjective impression, the categorized psychological evaluation is grasped quantitatively as the fuzzy event. That is, the so-called membership function in the field of fuzzy set theory is used as a method for discussing the relationship between the objective acoustical stimulus and the subjective human response. The set of eight simplified patterns of membership functions is first established by using the data obtained from an actual psychological experiment in the case when the test subjects are exposed to the octave-band-limited white noise with center frequency f(cK) (K = 1, 2, ..., 8). Next, the membership functions for the psychological impression are estimated by use of the above set of eight simplified patterns, in a case when the test subjects are exposed to art arbitrary non-white random noise. Further, a method for evaluating the psychological response is proposed by using the concept of the fuzzy probability. Finally, the validity and the usefulness of the proposed method are confirmed experimentally by applying it to the actually observed data. Copyright (C) 1996 Elsevier Science Ltd