In the microbiological investigation, made on samples of normal; (n=412) and mastitic (n=482) milk, proceeded from eight dairy cows farm, in Transilvania, it was signal the presence of the algae without chlorophyl belonging to Prototheca, forming together with bacteria and fungi the micro flora of the mammary gland. The alga content of normal milk was signaled only in two farms (2.27%, respectively 1.21%), being established to 0.72%. In the case of mastitic milk the percentage of positive samples raised up to 3.3%, the isolating frequency being important only in one farm (9.6%), where were episodes of antibiotic resistant mastitis. The alga were well developed on gelose and Sabouraud agar, at 20-37°C, and their identification as Prototheca, was based on making evident the typical morphological elements, big sporangium (10-30μm) containing 4-8 daughter cells.