The current consumption of glycerol is not enough to use all the glycerol that can be generated by high production levels of biodiesel, which could lead to irresponsible disposal of this residue in the environment. An alternative to consuming part of the glycerol produced is its use in animal feeding. An important assessment to be made before adding any ingredient in the diet of ruminants is if the new ingredient causes some change in the kinetics of ruminal organic matter. In this context, increasing levels of crude glycerin (0, 30, 60, 90, 120, 150, 180, 210 and 240 g kg-1 dry matter) were included in isonitrogen and isocaloric diets formulated to meet the nutritional requirements of a 300 kg beef cattle gaining 1.2 kg d -1, in order to evaluate possible effects of glycerol on the in vitro kinetics of organic matter degradation, pH and ammonia ruminal levels, and microbial protein production. The experimental design was completely randomized with nine treatments and three replications. The maximum volume of gas produced by soluble and insoluble fractions, the rate of gas production by the degradation of the soluble fraction and insoluble fractions, the latency, the ruminal pH, the production of ammonia and of microbial protein did not differ among levels of glycerin. In contrast, the in vitro digestibility of dry matter, the organic matter and the fiber showed a linear increase with the inclusion of glycerin.