Background/Objectives: Reports on oral frailty as a risk factor for chronic constipation are scarce. In this study, we examined the relationship between Oral Frailty Index-8 (OFI-8) and constipation severity. Methods: This cross-sectional analysis involved patients aged >/=65 years (outpatients between November 2020 and November 2021). Patient background (age, sex, body mass index, medical history, lifestyle history, and oral medications), a constipation severity questionnaire (Constipation Scoring System [CSS]), grip strength, walking speed, skeletal muscle mass index (dual-energy X-ray absorptiometry), a frailty questionnaire, an oral frailty questionnaire (OFI-8), an abdominal symptoms quality of life (QOL) questionnaire (Izumo scale), a swallowing evaluation questionnaire (10-item Eating Assessment Tool [EAT-10]), a chronic obstructive pulmonary disease (COPD) evaluation questionnaire (COPD assessment test [CAT]), a simplified QOL evaluation (EuroQol-five dimensions [EQ-5D]), the Dietary Variety Score, a nutritional evaluation (CONtrolling NUTritional Status [CONUT] score), and the 15-item Geriatric Depression Scale (GDS-15) were analyzed. Risk factors for constipation severity (CSS) were examined using multivariate analysis. Patients with advanced gastrointestinal cancer, inflammatory bowel disease, and active gastroduodenal ulcer were excluded. Results: In total, 1029 patients (male/female: 450/579; mean age: 78.3 +/- 6.1 years; mean body mass index: 22.9 +/- 3) were included. Multivariate analysis demonstrated a significant association between CSS and OFI-8 (beta = 0.065), EAT-10 (beta = 0.061), sarcopenia (beta = 0.050), laxative (beta = 0.126), constipation-related QOL score (beta = 0.625), diarrhea-related QOL score (beta = -0.064), and CAT (beta = 0.061). Conclusions: Comprehensive risk factors associated with CSS included a high oral frailty score, impaired swallowing (EAT-10), sarcopenia, laxative use, a high constipation QOL score, a low diarrhea QOL score, and COPD assessment through CAT.