The research of the influence of zeolite on the growth and housing conditions in pig fattening was conducted on two groups of PIC race fatteners of line 337, at PGO Domagoj. There were 250 pigs in each group. In the experimental group, 2.5% zeolite was added to the mixture throughout the fattening period, and the zeolite was put on the concrete slatted floor in the amount of 300 g per pen every day. Control weighings of four randomly selected fatteners, out of a total of 19 which are in the pen, were performed on days 21, 42, 63, and 84, and throughout whole period was measured ammonia concentration at three heights (50, 160, and 200 cm from the floor). Statistically significantly higher average weights of pigs were recorded at both significance levels (P <0.05 and P <0.01) during all control weighings in the group which used zeolite. By the fatteners from the experimental group who were fed with zeolite addition, except better growth (total growth in the group with zeolite was 78.57, and in the control group 77.91 kg), better food conversion was recorded than in fatteners in the control group. During each measurement, statistically significantly lower concentrations of ammonia were recorded in the group in which the zeolite was sprinkled on the floor of the boxes, at both significance levels (95% and 99%) and at all measured heights (50, 160 and 200 cm from the floor). It can be concluded that the concentration of ammonia is reduced when using zeolite and that zeolite in food had a positive effect on fattening indicators, which justifies the use of zeolite in pig fattening.