This study was carried out to determine the role of some saprophitic fungi found in the horse faeces in the biological control of larval stages of small strongyles subfamilly Cyatostominac on these larvae. Interaction between the predacious conidia A. oligospora and third stage larvae were tested in vitro and under field conditions. This species of fungi at 2 colonies per 1OO, 200CC and 300CC 0.9% saline containing 300 third stage larvae can reduce significantly (P<0.000l) the number of Cyathostominae larvae by 49%, 34% and 37% respectively under laboratory conditions by using sticky branches and also by attachment of fungi conidia to the entire cuticle of the larvae. Three horses naturally infected with small strongly were each fed 120, 200 and 250 colonies of A. oligospora. The excreted dungs was collected on day zero, first, second and third day after administration of the colonies and the efficacy of fungi was assessed by counting the larvae in faecal culture in comparison with fungus free control pad. It was shown that the fungi can survive after passage through the gastrointestinal tract of horse and reduced the number of larvae in the horses that had received 250 colonies.