The growth rate and the proteolytic activity of Pseudomonas fluorescens strains 07A and 041, isolated from cow’s milk, were evaluated at 2, 4, 7 and 10ºC. P. fluorescens promoted protein degradation during storage of milk samples as observed by Proteolytic activity measurement, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and heat stability of milk. Casein hydrolysis resulted in loss of thermal stability of milk and in formation of fragments of low and medium molecular mass. Temperatures up to 10°C did not guarantee raw milk quality when contamination by P. fluorescens was equal or higher than 106 cfu/mL.