Background: MSP-1 is one of the potential malarial vaccine candidate antigens. However, extensive genetic polymorphism of this antigen in the field isolates of Plasmodium falciparum represents a major hindrance for the development of an effective vaccine. Therefore, this study aimed to establish the prevalence and genetic polymorphisms of K1, MAD20 and RO33 allelic types of msp-1 block 2 among P. falciparum clinical isolates from Lao PDR. Methods: Plasmodium falciparum isolates were collected from 230 P. falciparum-infected blood samples from three regions of Lao PDR. K1, MAD20 and RO33 were detected by nested PCR; SSCP was used for polymorphism screening. The nested PCR products of each K1, MAD20 and RO33 allelic types that had different banding patterns by SSCP, were sequenced. Results: The overall prevalence of K1, MAD20 and RO33 allelic types in P. falciparum isolates from Lao PDR were 66.95%, 46.52% and 31.30%, respectively, of samples under study. Single infections with K1, MAD20 and RO33 allelic types were 27.83%, 11.74% and 5.22%, respectively; the remainders were multiple clonal infections. Neither parasite density nor age was related to MOI. Sequence analysis revealed that there were 11 different types of K1, eight different types of MAD20, and 7 different types of RO33. Most of them were regional specific, except type 1 of each allelic type was common found in 3 regions under study. Conclusions: Genetic polymorphism with diverse allele types was identified in msp-1 block 2 among P. falciparum clinical isolates in Lao PDR. A rather high level of multiple clonal infections was also observed but the multiplicity of infection was rather low as not exceed 2.0. This basic data are useful for treatment and malaria control program in Lao PDR.