To identify deletion of large fragment in COL1A1/2 genes among patients with osteogenesis imperfecta (OI).Genomic DNA was extracted from peripheral blood samples by a standard SDS-proteinase K-phenol/chloroform method. Multiplex ligation-dependent probe amplification (MLPA) was performed to detect gross deletions of the COL1A1/2 genes among 46 patients affected with OI, in whom no mutation was detected in the sequences of the COL1A1/2 genes.Heterozygous deletions of the entire COL1A1 gene and exon 20 of the COL1A2 gene were detected in probands A and B, respectively, and no gross deletion was found in the remaining 44 samples. The MLPA result of proband A was confirmed by fluorescence quantitative PCR (Q-PCR) in his family. A further conjunction point analysis through gap-PCR and DNA sequencing revealed deletion of exons 17 to 23 in the COL1A2 gene, and a 637 bp-insertion from chromosome 5 in the proband B.Two gross deletions have been found in the genes coding for collagen type I in the Chinese OI population, and the deletion of exons 17 to 23 in the COL1A2 gene is a novel mutation. This work not only has expanded the mutation spectrum of the COL1A1/2 gene, but also provided a support for prenatal genetic diagnosis for the families.