Background Patient characteristics may be an internal factor influencing patient complaints, but in China patient characterization is restricted to patient satisfaction surveys, and few studies have considered the relationship between patient characteristics and patient complaints. The aim of this research was to determine the reasons for complaints. Methods In this study, we analyzed the characteristics of hospitalized patients and explored their relationship with medical complaints. Results The significant factors were age (P=0.045), hospital cost (P=0.003), household nature (P <0.001), and education (P <0.001). The complaint rate decreased when the patients' age increased (regression coefficient, -0.606; OR, 0.545, and 95%Cl, 0.301-0.987). The complaint rate increased with an increase in hospital cost (regression coefficient, 0.818; OR, 2.266; and 95%Cl, 1.320-3.889). Patients from non-agricultural households had a higher complaint rate (regression coefficient, 1.051; OR, 2.861; and 95%Cl, 1.611-5.082). Patients with higher education levels had lower complaint rates (regression coefficient, -0.944; OR, 0.389; and 95%Cl, 0.234-0.647). Conclusion The survey confirms that older patients and patients with higher education levels had lower complaint rates, while non-agricultural population and patients with higher hospital expenses had higher complaint rates. Chin Med J 2012;125(10):1790-1794