A study was conducted to evaluate the infection status of Blastocystis hominis in children from four public schools in Phuttamonthon district, Nakhon Pathom province, Thailand during November to December 2004. A total of 814 faecal specimens were used for B. hominis cultivation using Jones' medium. Mixed infections with other intestinal parasites were also examined by formalin ethyl acetate concentration method. It was found that 13.51% (110 of 814) of the children examined were infected with B. hominis. Mixed infections with other intestinal protozoa and helminths were observed in 10.91% (12 of 110) of B. hominis positive specimens. There were Giardia lamblia cysts (4.55%), Trichomonas hominis trophozoites (1.82%), Entamoeba histolytica cysts (0.91%), Endolimax nana cysts (0.91%), Strongyloides stercoralis larvae (0.91%), hookworm eggs (0.91%), and Trichuris trichiura eggs (0.91%). Of the children positive for B. hominis, there was no significant differences between sex (P > 0.05) and showed no correlation between age and the percentage of infection. The different infection rates among four schools indicated the involvement of hygienic factors which promoted the infection of this common intestinal protozoan. Variation in size of B. hominis was found in culture medium, which might indicate to the presence of different strains of B. hominis infection.