In order to study the value of sequential and quantitative analysis of chimerism in determination of optional time of donor lymphocyte infusion (DLI) and prediction of efficacy of DLI, six patients with leukemias who relapsed or failed of engraftment were treated with DLI. Serial and quantitative analyses of donor chimerism (DC) both prior to and following DLI were performed by multiplex PCR amplification of STR markers (STR-PCR) and capillary electrophoresis with fluorescence detection. The results showed that at the time of relapse or graft rejection, STR-PCR indicated the decreasing donor chimerism in all six patients, at levels ranging from 27.3% to 85.7%. The declining value of DC (<90%) was detected in four patients at 26 days before relapse or graft rejection diagnosed clinically. Therefore the decrease of value of DC can be identified the high risk of relapse or graft failure and can be used to guide DLI implementation at early stage. In this study the clinical response were seen in two patients, the value of DC in these patients increased with convertion to a predominant donor profile (>90%) or converted to stable FDC shortly after DLI, while in the patients without clinical response, the level of DC decreased persistently or declined after transient increase. Three patients without response received second DLI. It is concluded that the monitoring of chimerism is proved to be a valuable to determine the optional time point of DLI and to early evaluate the efficacy of DLI. Furthermore, it can present a rational basis for treatment of intensification in the patients who did not respond to first-line DLI treatment.