Quality of life (QOL) for patients with chronic gastritis (CG) is of interest worldwide and disease-specific instruments are needed for clinical research and practice. This paper focused on the development and validation of the CG scale under the system of Quality of Life Instruments for Chronic Diseases (QLICD-CG) by the modular approach and both classical test theory and generalizability theory. The QLICD-CG was developed based on programmed decision procedures including multiple nominal and focus group discussions, in-depth interviews and quantitative statistical procedures. Based on the data measuring QOL 3 times before and after treatments from 142 inpatients with CG, the psychometric properties of the scale were evaluated with respect to validity, reliability and responsiveness employing correlation analysis, multi-trait scaling analysis, factor analyses, t tests and also G studies and D studies of generalizability theory analysis. Correlation, multi-trait scaling and factor analyses confirmed good construct validity and criterion-related validity when using SF-36 as a criterion. The internal consistency α for all domains were higher than 0.70 except for the social domain (0.62). Test-retest reliability coefficients (Pearson r and intraclass correlations) for the overall score and all domains were higher than 0.80 except for the social domain (0.77), while they were ranging between 0.72 to 0.94 at facets level; The overall score and scores for all domains/facets had statistically significant changes (P<0.01) after treatments except for facets of social effects and sexual function with standardized response mean ranging from 0.04 to 1.03, but from 0.34 to 1.03 for the domain level scores. G-coefficients and index of dependability (Ф coefficients) confirmed the reliability of the scale further with more exact variance components, and decision information on number of items changing. The QLICD-CG could be used as a useful instrument in assessing QoL for patients with CG, with good psychometric properties including validity, reliability and responsiveness and also several advantages. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.