This study was conducted to analyze diet and health-related factors based on the income level of single-adult households using data from the Korea National Health and Nutrition Survey (KNHANES). Among those who participated in the 2016-2018 KNHANES, 951 single-adult households aged 19 to 64 were selected, and factors such as general characteristics, physical characteristics, dietary behaviors, health behaviors, and the prevalence of chronic diseases were analyzed. The high-income group had higher frequency of eating out, better dietary status generally, higher recognition rate of nutrition labels than the other groups. The rate of alcohol consumption and smoking was higher in the high-income group of single-adult households, while the rates of anxiety and depression were higher in the low-income group. Additionally, the use of dietary supplements decreased as income level decreased. Among chronic diseases, hypertension, diabetes, and dyslipidemia had the lowest prevalence in the middle-income group and the highest prevalence in the low-income group. These results suggest that diet and health behaviors vary by income level in single-adult households and may be associated with the prevalence of chronic diseases. Future systematic studies should be conducted to determine the causal relationships between these factors.