Activity of amylolytic, proteolytic, and lipolytic enzymes in the content and mucosa of intestinal tract, alkaline phosphatase in mucosa of intestinal tract, as well as the determination of calcium and phosphorous concentration in gastro-intestinal tract of hens were analyzed in the conditions of the Republic of Belarus. Results of analysis of the obtained experiment results of laying hens of parental stock by influence of various vitamin-mineral additives were presented. The highest activity of amylolytic, proteolytic, and lipolytic enzymes in 170-330 days old laying hens of Belarus-9 cross was marked in small intestine. There was stated the decreasing of enzymatic activity in proportion to removal from a stomach. At the same time, activity of alkaline phosphatase decreasds. Activity of alkaline phosphatase, proteolytic and starch-reducing enzymes in a mucous membrane of a duodenal gut was a bit higher than in mucosae of jejunal. Lipolytic enzymes showed high degree activity in mucosae of jejunal. Enzymic activity in large bowel was low. Addition of iodine-containing preparation Kajod into hen layer diets increased the activity of alkaline phosphatase, of amylolytic, proteolytic, and lipolytic enzymes in intestines. Enzymic activity of mucous intestines at hens of breed Plimutrok in process of removal from stomach decreased. In course of the period from 240 to 330-days old age the activity of studied enzymes in hen intestines decreased. Replacement of mineral additive Cockleshell by Pikumin did not render negative influences on changes in digestive enzyme activity. In 170-days old laying hens of Belarus-9 crossbreed the calcium content increased from the stomach to the small intestine, and then decreased in thick department. In the 200-days old hens the calcium concentration in a stomach increased in both groups and gradually decreased in the department of small intestine, but in rectum its quantity increased in both groups. In the period of intensive egg-laying (280 days) the general calcium content in thin department of intestines was less than in the stomach, later it increased in cecum and decreased in rectum. By the end of the experiment (330 days) the concentration of calcium in control group decreased from the stomach to the beginning of thick department of intestines, but in rectum its quantity increased. In experimental group the calcium content increased from a stomach to cecums and then decreased in rectum. In distribution of inorganic phosphorus in gastrointestinal tract departments at hens of various age groups the tendency to increase in its quantity in small intestine and the beginning of thick department of intestines, and then to reduction in rectum was observed. And at hens receiving premix Ajdeko, the phosphorus content, since 200-day age, was higher, than at hens receiving the basic ration