There were 5 ant species which were known as intermediate hosts of tapeworm Raillietina spp found in raising backyard chicken in Thai Nguyen province - Viet Nam, namely Pheidologeton diversus, Tetramorium caespitum, Camponotus nicobarensis, Camponotus treubi, Anoplolepis gracilipes. These species belongs to Formicidae family. Appearance frequency of five species in the ecological areas was from 66.67 percent - 100 percent. 127 out of 144 (88.19 percent) ant colonies transferred tapeworm proglottis in chicken feces to the nest. The ant was more active in finding the food between 7 am - 10 am (78.47 percent). The rate of ants carrying Cysticerrcoid larvae was 40.83 percent. The ant did more activity as well as brought more tapeworm proglottis in the summer - autumn season than winter - spring. Tetramorium caespitum ant was infected with eggs of tapeworm Raillietina spp. Cysticercoid was first found in infected ant after 28 days and after 30 days, Cysticercoid occurred in all of samples. The average number of Cysticercoid per sample after 30 days was from 83 - 112 Cysticercoid.