<b>(1) Background:</b> Hematologic malignancy patients have a heightened risk for prolonged COVID-19 pneumonia. <b>(2) Methods:</b> We retrospectively investigated the clinical significance and serial CT findings of prolonged COVID-19 pneumonia in hematologic malignancy patients. Hematologic malignancy patients with persistent SARS-CoV-2 polymerase chain reaction (PCR) positivity >30 days and more than one chest CT after initial positivity were reviewed. Serial CT images were analyzed for the presence of COVID-19 pneumonia, patterns and distribution of CT findings, and severity scores of lung involvement. Clinical characteristics of the patients, including treatments for underlying hematologic malignancy prior to and after COVID-19 and COVID-19-related factors, were compared according to the presence of COVID-19 pneumonia. <b>(3) Results:</b> A total of 55 patients (36 male, median age 60 years) were included in the study. A total of 56.4% had received B-cell-directed therapies, such as rituximab or teclistamab, within one year of COVID-19 diagnosis. A total of 76.4% of patients had the presence of COVID-19 pneumonia on CT, with a median CT duration of pneumonia of 35.5 days, and they experienced more frequent (<i>p</i> = 0.005) and longer (<i>p</i> = 0.002) hospital stays and longer delays in treatment for underlying malignancy (<i>p</i> = 0.03), compared to those without evidence of COVID-19 pneumonia on CT. The development of COVID-19 pneumonia was significantly related to B-cell-directed antibody therapies (<i>p</i> = 0.02). Median CT severity scores during <30 days, 30-59 days, 60-89 days, and ≥90 days from initial diagnosis were 2.0, 2.0, 2.0, and 1.0, respectively. <b>(4) Conclusions:</b> Patients with hematologic malignancies may experience prolonged COVID-19 pneumonia, which is associated with the use of B-cell-directed antibody-based drugs and can result in longer hospital stays and delays in treatments for underlying malignancy.