To establish questionnaire scaling and reliability and examine the clinical and psychometric validity of the quality of life assessment based on Traditional Chinese Medicine for advanced gastric cancer (QLASTCM-Ga). The QLASTCM-Ga was developed based on programmed decision procedures with multiple nominal and focus group discussions, in-depth interview, pretesting and quantitative statistical procedures. The questionnaire was administered to 240 patients diagnosed with advanced gastric cancer before and after treatment. Structured group methods were employed to establish a general and a specifific module respectively. The psychometric properties of the scale were evaluated with respect to validity, reliability and responsiveness. The three identified scales of the QLASTCM-Ga and the total score demonstrated good psychometric properties. Test-retest reliability of the total scale and all domains ranged from 0.90 to 0.94, and internal consistency ranged from 0.86 to 0.93. Correlation and factor analysis demonstrated good construct validity. Signifificant difference in the subscales and the total score were found among groups differing in traditional Chinese medicine syndrome, supporting the clinical sensitivity of the QLASTCM-Ga. Statistically signifificant changes were found for each scale and the total score. Responsiveness was also good. The QLASTCM-Ga demonstrates good psychometric and clinical validity to assess quality of life in patients with advanced gastric cancer undergoing traditional Chinese medicine therapy. This study is an important fifirst step for future research in this area.