Diarrhoea in suckling and weaned pigs was the most important cause of economic losses in a Piglet Production Unit (PPU) in the State of Rio Grande do Sul, Brazil. Yellowish liquid feces were seen in the maternity and nursery floors and on the piglets bodies. The PPU had as routine the use of toltrazuril for the control of coccidiosis at the first week of life of the piglets, also it was used injection of gentamycin into all the piglets from the litter when there was the occurrence of diarrhoea. Facing this problem, because the procedures did not improuve the health and did not reached the control of diarrhoea, increasing economic losses, were collected rectal swabs from piglets presenting liquid feces, from maternity and nursery, 30 samples/ week, for five weeks, in a total of 155 samples, being 97 from suckling pigs and 58 from weaned pigs. Material was submitted to bacteriology in the Laboratory of Bacteriology from the University Veterinary Hospital. It was isolated 13 strains of haemolytic E. coli and 140 non haemolytic E. coli. The results of the antimicrobial susceptibility tests (AST) showed resistence of E. coli to the previous treatment of routine. The use of antimicrobials shosen by AST was effective for the control of colibacilosis.