The purposes of this study were to investigate the relationship between sarcopenia and phase angle (PhA), and to examine whether PhA cutoff values can be used to identify sarcopenia in patients with hematologic malignancies. The study population comprised 108 patients with hematologic malignancies who were admitted for chemotherapy, and were undergoing rehabilitation for exercise therapy. The diagnostic criteria for sarcopenia were determined according to the Asian Working Group for Sarcopenia 2019. Muscle strength, endurance, and body composition (including PhA), were assessed. Logistic regression and receiver operating characteristic (ROC) curve analyses were performed to investigate associations between sarcopenia and PhA, and to determine cutoff values. Sarcopenia was found in 17.6% of the participants. PhA was significantly associated with sarcopenia (p < 0.01). The areas under the curve were 0.84 for the males and 0.87 for the females, and the cutoff values were 4.75° for the males (sensitivity 69%, specificity 83%) and 3.95° for the females (sensitivity 78%, specificity 85%). Our results suggest that PhA, which can be measured noninvasively, objectively, and rapidly, can be used as a screening tool for sarcopenia in patients with hematologic malignancies.