We studied the ultrastructure of the spermatozoon of northern grass lizards ( Takydromus septentrionalis , n = 5) collected in April 2003 from a population in Wenzhou, Zhejiang, eastern China. The mature spermatozoa are characterized by: A circular acrosome; an acrosomal vesicle divided into cortex and medulla; the unilateral ridge of the acrosome vesicle divided into cortex and medulla, the electron-lucent zone between them; a prenuclear perforatorium, absence of the perforatorium base plate; presence of the subacrosomal space; an elongated nucleus, absence of a endonuclear canal; absence of epinuclear lucent zone; rounded nuclear shoulders. A bilateral stratified laminar structure within the neck region. A short midpiece; absence of multilaminar membranes; in longitudinal section, two tiers of mitochondria, in transverse section, six mitochondria with linear cristae; the presence of two dense body groups, the ring structure consisting of the complete ring; the arrangement pattern of the ring structure and mitochondria in rsl/mil and rs2/mi2; a fibrous sheath in the midpiece; presence of an annulus. A thin granular zone of cytoplasm at the anterior portion of the principal piece; the enlarged fiber 3 and fiber 8 disappearing at the anterior portion of the principal piece; the axoneme complex having an usual 9 + 2 pattern. Within lacertid lizards, sperms differ among species in the number of mitochondria, but in all species studied so far, there are two groups of dense bodies. However, lizards of different taxa differ, in various degrees, in such sperm morphological traits as acrosome vesicle, subacrosomal space, epinuclear lucent zone, perforatorium base plate, nuclear shoulder and number and arrangement of mitochondria and dense bodies. These differences suggest that sperm morphology provides additional information which one may use to study the phylogeny of lizards.