Resumo. The present work aimed to study the fitossociologic structure and floristic similarity among seasonal and mixed forests of Argentina and Brazil. Cruce Caballero Park with 522 hectares where the method of multiple plots was adopted with (20 x 10 m). In each plot all individual tree of size equal or heigher than 5 cm diameter were registered, being measured the stem diameter and height into three environmental compartments, Haplorthox, Ustorthent and Udorthent. In Haplorthox, Araucaria angustifolia (Bertol.) Kuntze prevail at higher stratum and Sorocea bonplandii (Baill.) W.C.Burger, Lanj. & Boer, Cabralea canjerana (Vell.) Mart., Ocotea lancifolia Mez and Apuleia leiocarpa J.F.Macbr. follow it. In Ustorthent araucaria is absent and Gymnanthes concolor Müll.Arg., Trichilia claussenii C.DC., Apuleia leiocarpa, Pilocarpus pennatifolius Lem. and Sorocea bonplandii prevail. Aracuaria is scarce in Udorthent where Parapiptadenia rigida (Benth.) Brenan, Alchornea triplinervia Müll.Arg., Luehea divaricata Mart., Erythrina falcata Benth. and Myrsine gardneriana A.DC. prevail. A comparative analysis shown Cruce Caballero more similar to seasonal forests than mixed araucaria forest from Brazil.