The karyotypes of thirteen species of Uruguayan ants belonging to three different subfamilies (Myrmicinae, Dolichoderinae and Formicinae) are reported. Among eight myrmicines studied, the chromosome numbers of four species ofPheidole (P. cornutula, P. fallax, P. spinninodisandP. strobeli)were all 2n= 20 (orn= 10). A count of 2n= 32 (orn=16) was obtained forSolenopsis saevissima, while 2n= 38 occurred in three leaf-cutter ants of the genusAcromyrmex [A. (Acromyrmex) ambiguus, A. (A.) hispidusandA. (Moellerius) heyeri]. The one dolichoderinae ant examined,Conomyrma pyramica, had 2n= 18 and three species ofCamponotus, C. bonariensis, C. punctulatusandC. rufipes(Formicinae), showed a relatively high number 2n= 40 (orn=20) compared to that inC. mus(2n= 26).