Background Loneliness is a significant precursor to depression and other adverse health outcomes, particularly in rural primary care settings. This study explores the association between loneliness and biopsychosocial factors among regular patients in rural community hospitals, focusing on Unnan City, Japan. Methods A cross-sectional study was conducted among 647 patients over 40 who regularly visited the general medicine department of Unnan City Hospital between September 1, 2023, and November 31, 2023. Data were collected using the Japanese version of the three-item University of California, Los Angeles (UCLA) Loneliness Scale and self-reported questionnaires on social behaviors, agricultural activities, community participation, eating habits, and physical health metrics. Logistic regression models identified factors associated with higher loneliness. Results Higher loneliness was significantly associated with frequent community dialogue (OR=2.43
95% CI: 1.70-3.46
p<
0.01) and frequent agricultural activities (OR=1.92
95% CI: 1.27-2.90
p<
0.01). In contrast, regular participation in community activities (OR=0.55
95% CI: 0.39-0.79
p<
0.01) was associated with lower loneliness. Lower BMI was also associated with higher loneliness (OR=0.95
95% CI: 0.91-0.99
p=0.039). Conclusion Both social behaviors and physical health factors influence loneliness among rural patients. Effective interventions should emphasize the frequency and quality of social interactions, promote meaningful community participation, and consider physical health indicators like BMI. These findings can inform targeted strategies to reduce loneliness and prevent depression in rural healthcare settings.