Residual inhibition(RI) is defined as persistence of masking effect upon tinnitus after cessation of masking and is expected in masking method of treatment of tinnitus. For clarifying influencing factors on RI and difference of duration and rate of RI by different masking method, RI was examined by various methods of masking. Results were as follows ; 1) Among all conditions of masking, group of band noise masking with 30dB above MML for 1 minute had maximum in rate of RI(75.0%), group of white noise masking with 30dB above MML for 1 minute was next in rate(73.7%). And group of pure tone masking 10dB above MML for 1 minute had minimum in rate(52.7%) and there was significant difference between above mentioned 2 groups and this. With same conditions of intensity and time of masking, groups of pure tone masking had lower rate in RI than groups of white noise masking and groups of band noise masking. With same masking sounds, rate of RI was ranked as mentioned below;groups of masking with 30dB above MML for 1 minute, groups of masking with 10dB above MML for 1 minute and groups of masking with 10dB above MML for 10 minute. 2) Groups of band noise masking with 10dB above MML for 10 minute had maximum duration of RI(45.6 sec.) and group of white noise masking with 30dB above MML for 1 minute had minimum duration of RI(38.3 sec.), but duration of RI showed no significant difference between 2 groups. 3) Recovery time of tinnitus had no significance of difference of duration among groups. 4) In all conditions of intensity and time of masking, groups of band noise masking were longer in duration of RI than groups of white noise masking. 5) Rate of RI was increasing tendency by age. 6) No difference of rate of RI was showed among causative diseases and positive and negative SISI test. And the shorter duration of tinnitus, the more rate of RI. 7) 8000Hz frequency tinnitus was lowest in rate of RI(40.0%) and had significant difference from other frequency groups. And 0dB intensity tinnitus was lowest in rate of RI (40.0%) and had significant difference from 5dB or above intensity tinnitus. 8) Among Feldmann's types of masking curve, congruence type was most common(35.7%) and covergence type was next(30.0%) in order, but no significant difference in rate of RI was seen between 2 types. So author concluded that influencing factors of RI are age of patient, duration of tinnitus, frequency and intensity of tinnitus, and masking sound. And author recommends band noise masking with 30dB or 10dB above MML for 1 minute as method of RI test.