Common bean (Phaseolus vulgaris L.) is one of major plant protein sources for human food. Several diseases affect its yield and quality. Common bacterial blight (CBB), caused by Xanthomonas campestris pv. Phaseoli (Xap), is a seed born disease. One major source of resistance for CBB derived from tepary bean (P. acutifolius) was introduced into common bean. A major CBB resistance QTL, derived from XAN159 and originally from tepary bean line PI319443, is carried in germplasms HR45 and HR67 developed from our bean breeding program. Results showed that this major QTL can explain about 50% phenotypic variation. Five markers, including SCAR UBC420, STS333a, STS330c, STS283c and SSR PV-tttc001, were identified tightly linked to this major QTL within 5 cM. They were located on the distal region of chromosome 1L. Given the intensive utilization of this major CBB resistance QTL in breeding programs in the America, BAC library were constructed from the high molecular weight HR45 DNA partially digested using HindIII. The BAC library contains 33024 clones averaged at 100 kb. All of them were used to screen the BAC pools except STS330c (linked in repulsion). Based on available data, nine BAC clones are positive for UBC420 marker with size around 50 kb; eight BAC clones are positive for STS33a marker; three BAC clones are positive for PV-tttc001 marker and nine BAC clones are positive for STS183. One BAC clone p6g22 was confirmed positive to both STS183 and PV-tttc001. Over 2000 F2 plants from the cross HR45/OAC Rex are under investigation to fine map this major QTL. Contigs covering this major QTL will be assembled. Gene specific primers will be designed to facilitate the marker-assisted selection for the major QTL. The progress of cloning this major CBB QTL will be presented.