Abstract: CP23 gene of Cryptosporidium parvum was expressed in Escherichia coli， and the recombinant protein was purified. Its immunoreactivity was analyzed by Western blotting. Serum samples were collected from outpatients of different ages from August to November, 2010 in Changchun. Indirect ELISA was established to detect the anti-CP23 IgG in sera. Western blotting analysis indicated that the recombinant CP23 protein was recognized by sera from Cryptosporidium parvum-infected calves and positive human sera, but not recognized by sera of mice infected with Schistosoma japanicum, sera from falciparum malaria patients and negetive human sera. The overall anti-CP23 IgG positive rate was 3.2% （65/2 046）. The seropositive rate was 2.7% （28/1 036） in men and 3.7% （37/1 010） in women （P>0.05）. The seropositive rates were significantly different among age groups （P<0.05）, and the age group of 71-80 had the highest positive rate （8.6%, 13/152）.

Key words: Cryptosporidium, CP23, ELISA