Purpose: Patients’ complaints can be predictors of patient care quality and safety.Understanding patients’ complaints could help healthcare organizations target the areas for improvements.The purpose of this study is to use a mixed method analysis to a) examine the characteristics and categories of patients’complaints,b) explore the relationships of patients’ complaints with professions and units,and c) propose theory-based strategies to improve care quality.Methods: This is a descriptive mixed method study.Data examined are patients’ complaints filed at a university-affiliated hospital in China from January 2016 to December 2017.A qualitative content analysis was conducted to categorize complaints.A TwoStep cluster analysis was performed to provide an overall profile of patients’ complaints.Chi-Square tests were conducted to investigate the relationships among complaints,professions,and units.Results: 838 complaints were filed,with 821 valid cases for analysis.Six categories surfaced from the qualitative analysis: uncaring attitudes,unsatisfactory quality of treatment or competence,communication problems,the process of care,fees and billing issues,and other miscellaneous causes.Physicians received most of the complaints (56.6％).The unit receiving the most complaints were outpatient clinics and medical support units (52.7％).The cluster analysis indicated four distinct clusters.Significant relationships existed between complaints and professions (x2 (20)=178.82,P＜ 0.01),and between complaints and units (x2 (15)=42.72,P＜ 0.01).Conclusions: Patients’ complaints are valuable sources for quality improvements.Healthcare providers should be not only scientifically knowledgeable,but also humanistic caring.Caring-based theories may provide guidance in clinical practice.