Inclusion Criteria:

- Signed and written informed consent provided by patients ≥ 20 years old or by the
parents or guardians of patients less than 20 years old. Investigator should
verbally obtain informed assent from the patients 7 years old or older and written
informed assent from patients 12 years old or older.

- Greater than or equal to 25 percent blasts present in the bone marrow and/or
peripheral blood count and diagnosed with ALL .at time of enrollment

- Patients with relapsed or refractory ALL. Patients must not be eligible for therapy
of higher clinical benefit potential and must be in second or subsequent relapse
and/or refractory, i.e. failed to achieve remission following 2 or more different
regimens, or for whom no other therapy with greater potential clinical benefit
exists.

- Have a Karnofsky Performance Status of greater than or equal to 70 for patients 10
years of age or older or Lansky Performance Status greater than or equal to 70 for
patients below 10 years of age.

- Patients whose hepatic, renal, and pancreatic functional tests are within the ranges
defined in the protocol.

Exclusion Criteria:

- Received previous treatment with clofarabine.

- Have received any other investigational agent within 30 days prior to the first dose
of the study drug.

- Have received any other chemotherapy within 14 days prior to the first dose of
clofarabine. However, intrathecal drug administration is allowed up to 24 hours
prior to the first dose of clofarabine. In addition, the patient must have been
recovered from acute toxicity related to other chemotherapy or investigational agents
(baseline or less than or equal to Common Terminology Criteria for Adverse Events ver
3.0 Grade 1)

- Have systemic fungal, bacterial, viral, or other infection that cannot be
controlled(defined as exhibiting ongoing signs/symptoms related to the infection and
without improvement, despite appropriate antibiotics or other treatment). In
addition, for patients with a history of fever (≥38.5˚C) within the preceding 3 days
at the time of enrollment, documentation of negative blood cultures for at least 48
hours required.

- Have a psychiatric disorder that would interfere with consent, study participation,
or follow-up.

- Patients whose spinal fluid tested immediately before the study registration within 7
days before dose indicates symptomatic Central Nervous System (CNS) involvement
(i.e.CNS3).

- Have any other severe concurrent disease or a history of serious organ dysfunction or
disease involving the heart, kidney, liver, or pancreas.

- Have received hematopoietic stem cell transplantation (HSCT) within 3 months prior to
providing the consent or have acute graft-versus-host disease (GVHD) (greater than or
equal to Grade 2) requiring immunosuppressive therapy or severe (systemic) chronic
GVHD.

- Have a prior positive test for Hepatitis B surface (HBs) antigen or antibody, HBc
antibody, Hepatitis C virus (HCV) antibody, or human immunodeficiency virus (HIV)
antibody. (The patients who have had treatment of vaccine and are positive for HBs
antibody are eligible).

- Are pregnant or nursing. Male and female patients of reproductive potential must
agree to use an effective means of birth control to avoid pregnancy during the study
period and for 180 days after the last dose of study drug.