The objective of the present work was to study probiotic fermented milks during fermentation process and cold storage. Two strains of probiotic bacteria were used: Lactobacillus acidophilus (LA) and Bifidobacterium animalis subsp. lactis (BL). The yogurt culture Lactobacillus bulgaricus (LB) was used as control. All strains were employed in coculture with the starter Streptococcus thermophilus (ST). Commercial skimmed milk powder was diluted in distilled water (12.4g 100g -1 ) and heat treated. All inoculated milks were incubated for fermentation at 42°C in a water bath until pH 4.50 was reached. Chemical changes during fermentation were followed by measuring: V m (maximum acidification rate that measures the decrease of pH units per minute and the values are expressed as mUpH/min), t Vmax (time to achieve the maximum acidification rate, in h), t pH5,0 (time to achieve pH5.0, in h) and t pH4.5 (time necessary to reach pH 4.5, in h). Rheological behavior was determined at d1 and firmness, pH and viability were followed until 28 days of storage at 4ºC. Fermentation time for probiotic cultures was longer than for yogurt culture. pH decreased and firmness increased during storage. The main change occurred in the first week. Probiotic bacteria grow during fermentation. ST dominated over the other strains and remained stable during all storage period. B. lactis and L. bulgaricus attain the final storage period stable. L. acidophilus, however, decreased before 14 days of storage and at d 28 doesn't fit the minimum requirements to achieve beneficial properties to health.