Researchers investigated the relationship between three nutritional indicators, the Mini Nutritional Assessment-Short Form (MNA-SF), Geriatric Nutritional Risk Index (GNRI), and Controlling Nutrition Status (CONUT), and physical activity at discharge in patients admitted to convalescent rehabilitation wards. The research included 1601 patients (77 ± 12 years, male 46.2%) discharged from convalescent rehabilitation wards between April 2018 and September 2023. MNA-SF, GNRI, and CONUT scores were obtained on admission. Patients were divided into two groups according to their level of Functional Independence Measure (FIM) walk score at discharge. The walking group (n = 1181, FIM walk score ≥ 5, 76 ± 13 years, male 47.2%) was significantly younger than the wheelchair group (n = 420, 79 ± 12 years, FIM walk score < 5, male 43.8%) and had significantly higher MNA-SF (6.5 ± 2.5 vs. 4.7 ± 2.4) and GNRI (93.1 ± 12.4 vs. 86.7 ± 10.9) scores and significantly lower CONUT (3.1 ± 2.3 vs. 3.9 ± 2.3) scores than the wheelchair group (all p < 0.01). Multivariate logistic regression analysis showed that age, handgrip strength, Functional Oral Intake Scale, and MNA-SF score were independently associated with walking ability at discharge (all p < 0.01). In addition, MNA-SF scores were independently associated with Rehabilitation Effectiveness. These results suggest that nutritional status, particularly MNA-SF scores on admission, is associated with improvement of physical activity at discharge.