The present work was designed to study the ultrastructure of buffalo bull spermatozoa and to recognize the possible defects that may occurre following the cryopreservation process. Fresh semen samples were collected from three buffalo-bulls from Mahallet Musa buffalo research station in Kafr El-shiekh Governorate for production of buffalo-bull sires. Straws of cryopreserved semen were obtained from Kafr El-Shiekh Center for frozen buffalo-bull semen. All these samples were prepared for examination by transmission electron microscope. The results revealed that the freshly collected spermatozoa from apparently healthy buffalo bull consisted of head and tail. The tail attached to the head axially and consisted of neck, middle piece, principle piece and end piece. The head consisted of the acrosome and the nucleus surrounded by the plasma membrane. The neck located between the head and middle piece and had fossa in which the centriole was located. The middle piece was characterized by the mitochondrial sheath that surrounded the flagellar core in 9+2 axonemic arrangement and the nine outer dense fibers (ODF). The principle piece was the longest portion of the spermatozoon. It had flagellar core, dense fibers and fibrous sheath. The fibrous sheaths were made of two longitudinal columns, a dorsal and a ventral one, and connecting ribs. The end piece contained only the axial filament complex. The results revealed the effect of cryopreservation on ultrastructure of buffalo bull spermatozoa; disruption, undulation and damage of plasma membrane, detached and disintegration of acrosome, decondensation of chromatin of the nucleus, bent and swelling middle piece, breakage of the plasma membrane of middle piece and loss of some of the mitochondria, irregular shaped mitochondria, irregular arrangement and shape of dense fibers and distorded axonemes.