Inclusion Criteria:  1. Adult patients (20 years of age) have the following three subtypes of PTCL:  (1)Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), (2)Angioimmunoblastic lymphoma (AITL), or (3)Anaplastic large cell lymphoma (ALCL). If patients had CD30-positive systemic ALCL, they should receive brentuximab vedotin before enrollment 2. (1) In transplant-eligible patients: patients who have relapsed disease after autologous stem-cell transplantation (2) In transplant-ineligible patients: patients who have received at least first-line systemic chemotherapy treatment and have a stable disease, progressive disease, or relapsed disease.  3. Patients have an ECOG Scale of Performance Status score of 0-1. 4. Patients have at least one measurable lesion by CT with a size of > 1.5 cm in at least one axis.  5. Patients have adequate renal function: serum creatinine (Cr) ≤ 1.5 times the upper limit of normal range (ULN) and calculated creatinine clearance (Ccr) ≥ 40 mL/min.  6. Patients have adequate bone marrow function:  Absolute neutrophil count (ANC) ≥ 1500/μL, Without growth factor support (filgrastim or lenograstim) for at least 14 days Platelet count ≥ 75 000/μL. Evaluated at least 7 days after last platelet transfusion Hemoglobin ≥ 8 g/dL. May receive transfusion 7. Patients have adequate hepatic function: serum alkaline phosphatase (ALP), alanine, or aspartate aminotransferase levels (ALT & AST) ≤ 2.5 times the ULN and serum total bilirubin ≤ 1.5 times the ULN.  Exclusion Criteria:  Patients have already been exposed to lenalidomide and gemcitabine. Patients have less than 100 days from previous autologous stem cells transplantation prior to first study drug dose. Patients have HIV infection. Patients have cerebral or meningeal disease including signs or symptoms of progressive multifocal leukoencephalopathy. Patients have symptomatic neurologic disease compromising normal activities of daily living or requiring medication. Patients have any active systemic viral, bacterial, or fungal infection requiring systemic antibiotics within 2 weeks prior to first study drug dose. Patients received prior immunosuppressive chemotherapy, therapeutic radiation, or any immunotherapy (eg, immunoglobulin replacement, other monoclonal antibody therapies) within 4 weeks of first study drug dose. Patients have known hypersensitivity to any excipient contained in the drug formulation of lenalidomide or gemcitabine. Patients have known positive hepatitis B surface antigen but not receive anti-hepatitis B drug, or known or suspected active hepatitis B and C infection. Patients have diagnosed or treated for another malignancy within 3 years before the first dose or previously diagnosed with another malignancy and have any evidence of residual disease. Patients with nonmelanoma skin cancer or carcinoma in situ of any type are not excluded if they have undergone complete resection.  Patients have any of the following cardiovascular conditions or values within 6 months before the first dose of study drug:  A left-ventricular ejection fraction <50%. Myocardial infarction within 2 years of randomization. New York Heart Association (NYHA) Class III or IV heart failure Evidence of current uncontrolled cardiovascular conditions, including cardiac arrhythmias, congestive heart failure (CHF), angina, or electrocardiographic evidence of acute ischemia or active conduction system abnormalities. Patients with unstable medical or psychiatric conditions or a history of any other serious medical disease deemed inappropriate for inclusion in this study, as determined by the investigators. Women who are pregnant or breastfeeding or have a positive pregnancy test during screening or Day 1 before the first dose of study drug. Women of childbearing potential who do not use two effective contraceptive methods from the time of signing informed consent through 6 months after the last dose of study drug or agree to completely abstain from heterosexual intercourse. Male patients, even if surgically sterilized, (i.e., status post vasectomy) who do not agree to practice effective barrier contraception during the entire study period and through 6 months after the last dose of study drug, or agrees to completely abstain from heterosexual intercourse. Patients with a life expectancy of <3 months, as determined by the investigators. Patients with, as judged by the investigators, other contraindications for lenalidomide and gemcitabine administration, such as concurrent usage of drugs that may have potentially severe drug-drug interactions. Patients who are unwilling or unable to give consent.