The objective of the study is to check the validity and reliability of the instrument that is a significant modification of Retail Service Quality Scale (RSQS) and has been adapted for measuring service quality in branchless banking sector of Pakistan. Sample was cho-sen on the basis of purposive sampling. Primary data were collected through structured questionnaire. A total of 350 respondents from Islamabad and Rawalpindi participated in the study. Exploratory Factor Analysis (EFA) was first applied in order to suggest the dimensions of modified version of the instrument; then confirmatory factor analysis (CFA) based on maximum likelihood method was applied to check the validity and reliability of adapted items in the instrument. The results of EFA supplied the number of factors to be used in the study and CFA show model fitness. However, this study is limited to the extent of instrument development and testing using a small sample size so future research may be extended with large sample size for generalization.