Abstract: The present work is based on over 3000 specimens obtained from various localities in the Bilecik,Amasya and Gümüşhane - Bayburt regions, in northern Anatolia. The fossiliferous strata are within the range ofUpper Sinemurian - Lower Pliensbachian, extending up in Toarcian only in the Gümüşhane - Bayburt region. Thefamily Phylloceratidae are represented in these rocks by four genera : Phylloceras, Partschiceras Hantkenicerasand Calliphylloceras. The following species are identified: Phylloceras (Phy`loceras) frondosum, P(P). lipoldi, P(P).hebertinom, P(P). meneghinii, Phylloceras (Zetoceras) zetes, P(Z). pseudozetes, P(Z). bonarellii, P(Z). oenotrium,P(Z). lavizzarii, Partschiceras striatocostatum, Hantkeniceras cf. hantkeni, H. pseudocalais, Calliphylloceras bicicolae.In this first part, the species of Phylloceras are described. The second part, which is in preparation, willdeal with genera Partschiceras, Hantkeniceras and Calliphylloceras.