To characterize genetically the Campolina horse breed, 218 animals from different herds located in many Brazilian states were analyzed. For this study the serum proteins Albumin, Gc (vitamin D binding protein), Transferrin, Esterase and Xk (pre-albumin) were tested using starch gel electrophoresis and polyacrylamide gel electrophoresis (PAGE). The results indicated high number of homozygous animals in the Campolina breed, probably due to the intense use of some famous stallions.