The relationship between hypophosphatemia (HP) and malnutrition in older hospitalized patients has received little attention. We sought to investigate this association among this population. The study participants were consecutively admitted to a geriatric acute care ward in six hospitals. Malnutrition screening was conducted by Mini Nutritional Assessment-Short Form. Patients were divided into two groups according to serum phosphate: HP (<0.68 mmol/l) and non-HP groups (>0.68 mmol/l). Of 335 participants, 7% of subjects had HP. Malnutrition or nutritional risk was present in 86 and 56% of participants with and without HP, respectively (P = 0.003). The analysis indicated 9.8, 86.4, 97.9 and 44.0% sensitivity, positive predictive value, specificity and negative predictive value of HP with regard to malnutrition, respectively. This study demonstrated that HP in older hospitalized patients is associated with malnutrition and may be used as an indicator of nutritional risk. Contrary, normal serum phosphate does not exclude being at nutritional risk.