Lymphoma in the lung could be primary or secondary, nodal or extranodal, even Hodgkin's or non-Hodgkin's disease as presntation. Huge primary pulmonary lymphoma(HPPL) is rare in only 0.4%to 1% in all malignant lymphoma population. Now we submit a rare case with diffuse large B- cell type HPPL involving only left lung to see if any prognostic value of PET/CT scan after 6 cycles of chemotherapy.PET/CT scan shows no brain involvement or other lymph node spreading indicating good prognostic value of this patient. The tumor size of PET/CT scan is used to compared with previous CT scan to assure therapeutic response. Additional mediastinal hot spot was found to be related with local tumor invasion. The focal FDG avid spot is suggestive of SVC obstruction previously due to much paper reported for high incidence among high incidence among huge pulmonary lymphoma. By tracing the CT imaging of port-A insection line,there is no relationship between the focal FDG avid spot and port-A.So it suggests focal invasion caused by HPPL rather than SVC obstruction. The PET/CT scan also shows no apparent change after chemotherapy and suggestive of further radiothepary regimen for this patient. It also indicates poor prognostic value using chemotherapy regimen for this patient demonstrated by PET/CT scan.