A new lizard of the genus Tupinambis (Teiidae) is described based on specimens from Usina Hidrelétrica Três Irmãos, at lower Tietê river, between the municipalities of Araçatuba and Pereira Barreto (20035’ -20045’ S and 50015’ -51020’ W), State of São Paulo, Brazil. The specimens were obtained during fauna rescue to fill up the dam. Tupinambis palustris sp.nov. is mainly characterized by its ground color on dorsum, black intervened by small gray spots; black spots scattered on the gular surface and neck; large black spots scattered on belly; everted hemipenis shallowly forked with a well defined groove and two large petalas on each crown horn distally, larger than in T. teguixin, the closely related. In color, the new species also differs from other Tupinambis species of T. merianae group and T. teguixin by the absence of transverse banded pattern on back. It differs from T. quadrilineatus by the absence of whitish- yellow longitudinal narrow stripes on flanks, and from T. longilineus by the absence of a wide black band on flanks.
