The effectiveness of corrective maintenance actions performed on the repairable systems is utmost essential from reliability estimation point of view. According to generalized renewal process (GRP), any repair action brings a system either to as good as new (AGAN) or as bad as old (ABAO) or between AGAN and ABAO (intermediate) condition. These after repair conditions mathematically depend on repair effectiveness index (REI) denoted by ‘q’ as proposed by Kijima. In the literature, the methods are developed to estimate the value of q using only lifetime data of a system but in practical situations ‘q’ could be a function of many subjective factors which affect the repair quality while performing the repair action. This paper initially proposes nine factors which can affect REI the most followed by establishing a relationship of those factors with ‘q’ and provide modified REI value ‘qmod’. The selection of factors is done with the assistance of industrial maintenance experts. Theqmodcontains priority weights of each proposed factor which are estimated using fuzzy analytical hierarchy process (Fuzzy-AHP) and represents the overall effect of all factors on repair quality. The proposed methodology is demonstrated with the help of sensitivity analysis of each proposed factor with ‘qmod’ and an example.The application of the proposed methodology can be extended to any industry dealing with complex and critical repairable systems.