Background: The positive impact of imatinib on treatment outcome in Ph+ ALL is well known. The aim of this study was to evaluate the relationship between imatinib dose intensity and molecular response of BCR-ABL. Methods: Molecular response monitoring was performed at the central lab with quantitative RT-PCR assays for BCR-ABL RNA in serial; at the time of diagnosis, at hematologic complete remission (HCR), and every 3 months thereafter. The molecular response was defined as complete (MCR) if the BCR-ABL/G6PDH ratio was less than 1x10^-5. Results: Between October 2005 and February 2009, total 87 patients, aged 16-71 years, were enrolled with median follow-up of 5 years among survivors (range: 2.6-8.9 years). Eighty-two patients (94%) achieved HCR at a median 25 days (range, 14-69 days) and 45 patients (57.7%) of 78 evaluable patients achieved MCR at the same time. Within three months after induction treatment, 59 patients (67.8%) achieved MCR. Total MCR rate was 88.5% during the entire study period and the median time from treatment to MCR was 54 days (range, 13-384 days). Among these 77 MCR patients, 32 experienced molecular recurrence. After allogeneic HCT, 49 of 50 evaluated patients (98%) achieved MCR. Median time of MCR duration was 13 months (range, 0.9-60.3 months) and median molecular relapse-free survival (RFS) was 28 months. Thirty two patients who lost of MCR had significantly inferior RFS (P<0.0001) and OS (P=0.001) then 41 who maintained MCR. MCR achievement within 3 months after remission induction was significant predictor of RFS (P=0.004) and OS (P=0.003). Multivariate analyses after adjusting the Cox model was described in Table 1. Conclusions: Prospective assessment of molecular response and imatinib dose intensity is useful in identifying subgroups of Ph+ALL patients at a high risk of relapse. Clinical trial information: NCT00618501