This study is conducted in the field of animal of the Department of Livestock – College of Agriculture / University of Baghdad, and the practical part of the study for a period of five months begins in 13/08/2013 to12/1/2014 by using 29 Holstein Friesian cows . These cows are differed in the number of times of birth (parity) , and in the stage of lactation. The objective of the study is to study the effect of some environmental factors on the chemical composition of Holstein Friesian cows , the animals are fed on the same ration during the period of the study is based on a given animal you grass feed ( alfalfa or hay ) as well as concentrate feed and is focus on being the bush uniform for all studied animals and not to change components to the extent possible in order to affect the statement of other non- nutritional factors and their impact on the chemical composition of the milk, which is the desired goal of this study. The results show that there significant effect (p<0.05) at lactation stage on milk protein , as it records the highest percentage of protein 2.86 %in the third stage and the lowest percentage 2.79 % was in the second stage, while there were no significant differences a many the other components. Results also show significant effect (p<0.05) of season of year on the proportion of milk fat , with the highest percentage 3.34 % recorded in the spring season and the lowest 2.52 % in the summer , Also is record the highest percentage of milk sugar 4.24 % in the spring season and the lowest 4.07 % in summer, and there are no significant differences for protein and minerals of milk . also record significant effect (p<0.05) of parity on the components of milk , which is the highest percentage of fat 3.66 %in the first birth and the lowest percentage 2.67 %of the fourth calving , also the record the highest percentage of protein 2.86 % in the first calving and the lowest percentage 2.74 % in the third calving, also the first calving exceed the third in the percentage of sugar which is : 4.29 Vs . 4.09 % and it is 0.64 Vs. 0.61 % of metals .