The prevalence of helminths in adult sheep was investigated in Heilongjiang Province, People's Republic of China between January 1999 and September 2003. A total of 326 adult sheep representing local breeds (Xingjiang Fine Wool Sheep, Dongbei Fine Wool Sheep) as well as introduced breeds (Merino and Charollais) from representative geographical locations in Heilongjiang Province were slaughtered and examined for the presence of helminths. The worms were examined, counted and identified to species according to existing keys and descriptions. A total of 26 helminth species were found representing 2 phyla, 3 classes, 13 families and 20 genera. All sheep were infected by more than one helminth species. Oesophagostomum columbianum, Haemonchus contortus and Trichostrongylus colubriformis were the most common nematode species, and Paramphistomum cervi, Orientobilharzia turkestanica and Fasciola hepatica were the most common trematode species, whereas the infection of adult sheep with cestodes was uncommon. The results of the present investigation provide relevant "base-line" data for Heilongjiang Province, China, for assessing the effectiveness of future control strategies against helminth infections in sheep.