Background: Smoking and abdominal obesity are independent risk factors contributing to the global burden of diseases, which are major causes of morbidity and mortality. To date, it is unclear about the combined effects of obesity and smoking on respiratory muscle strength and lung function. The aim of this study was to examine the combined effects of abdominal obesity and smoking on respiratory muscle strength and lung function. Methods: Seventy‑two men aged 20–40 years were classified into four groups: control, obesity, smoking, and obesity plus smoking groups. Respiratory muscle strength and lung function were assessed and compared between groups. Results: Obesity plus smoking group evidenced the lowest levels of both respiratory muscle strength and lung function, followed by the smoking group and obesity group, relative to the control group (P < 0.01). Moreover, obesity status was significantly negatively correlated with lung function (r = −0.584, P = 0.001 for obesity group and r = −0.631, P = 0.001 for obesity plus smoking group). Smoking status showed a negative correlation with lung function (r = −0.397, P = 0.037 for smoking group and r = −0.706, P < 0.001 for obesity plus smoking group). Conclusions: The combination of obesity and smoking showed greater deterioration in respiratory muscle strength and lung function relative to obesity or smoking alone, and this is, therefore, likely to increase the risk of respiratory‑related chronic diseases. Thus, close monitoring of respiratory symptoms, primary prevention, and early management in individuals who are obese and smoking should be given priority concern.