During the microscopic anatomical study of a fresh water siluridfish, Wallago attu,a new trematode species Opisthorchis varunai was recorded from the gallbladder. The fish was collected from the Varuna River in Varanasi. The newly reported species has been described in detail, discussed and compared with other species of the genus Opisthorchis. It has elongated spinose body, bluntly pointed at anterior and posterior extremities, entire ovary, ventral sucker pre-equatorial, unlobed testes and presence of pre-pharynx. It has been distinguished by other species (...) through the absence of a crown of spines around the excretory pore. (shrink)