Neosporosis is an emergent disease in cattle, due to a protozoan called Neospora caninum. In adult cattle, the infection with Neospora caninum results particularly in abortions. The abortive role of this parasite was demonstrated for the first time in 1989. Since that, this role was confirmed in number of countries by several authors. The importance of this emergent disease as a principal cause of abortion increased the interest to search this unknown affection in livestock in Algeria. Thus a study has been conducted in order to detect neosporosis in bovine farms in the region of Constantine. The aim of this study is to search the antibodies of anti Neospora caninum using the technique ELISA in order to evaluate its prevalence in serum of cows having aborted or not tested serologically negative vis-à-vis of the main abortive diseases of cows in dairy cattle farms in Constantine. The results obtained show a prevalence of 16% of positive females to Neospora caninum. On the other hand, the seroprevalence of Neospora caninum in cows having aborted is 25%. This study shows that Neospora caninum is a parasite present in bovine livestock in Algeria. There is a need to evaluate the importance of this infection in a large number of breedings by seroepidemiological survey.