All over the world and also in Poland there are required definite demands at production of milk which included sanitary, process production and transport condition. The producers are obligated to make necessary procedure operations to correct quality and sanitary standards of raw milk. All this changes happened because of systematically growing consumers demands and business networks concerns about quality of ready-to-eat milk products, what is determined by quality and safety of raw milk. The aim of this study was to compare the microbiological quality and chemical composition in period from January to November in Wielkopolska region in 2004. The size of production of milk differentiates suppliers on two groups: small farms – less than 3 thousands litters per month, and big farms where 100 thousands litters of milk were produced over a month. The experimental material comprised samples of milk from 20 farms in each of analyzed size class of farms. The researches in bimonthly interspaces were done. In samples total number of microorganism (OLD), contents of somatic cells (KS), content of fat and proteins were estimated. In result differences in microbiological quality as well as contents of fat in raw milk in both of analyzed groups were proved. In milk samples from small farms count of total microorganisms on higher level were estimated. The somatic cells content in milk samples inside small farms group more diverse were observed. Similarly fat content was more differentiated in samples of raw milk at smaller production which depending on month of analysis in comparison with the second farms. The protein content in raw milk was depended on size of farms and also on month of analysis. The influence of size of farm and a season of the year on protein content in raw milk was also indicated.