We determined the effects of feeding different levels of a 50:50 molasses:crude glycerol supplement on ruminal fermentation and blood parameters. Eight ruminally cannulated Angus crossbred steers (323 ± 42 kg BW) were used in a 4 × 4 duplicated Latin square design. In each of the 4 28-d periods, animals were housed in individual pens at the University of Florida Feed Efficiency Facility, had ad libitum access to Tifton 85 bermudagrass hay, and were randomly assigned to one of 4 treatments: 0, 0.45, 1.36, and 2.27 kg/d (as fed) of a 50:50 liquid mixture of molasses:crude glycerol. Ruminal fluid and blood samples were collected before supplement feeding (0 h) and every 3 h postfeeding for 24 h. Immediately after each collection, ruminal pH was measured. Plasma was analyzed for blood urea nitrogen (BUN) and ruminal fluid for VFA and NH₃-N concentrations. Data were analyzed as repeated measures and orthogonal polynomial contrasts were used to determine the effects of supplementation level on ruminal fermentation and blood parameters. As the level of supplementation increased, mean ruminal pH (6.73, 6.83, 6.74, 6.65 for 0, 0.45, 1.36, and 2.27 kg/d, respectively; P = 0.03) and concentrations of BUN and NH₃-N (P < 0.001) decreased linearly. Molar proportions of acetate decreased (P < 0.001) whereas molar proportions of propionate (P < 0.001) and butyrate (P = 0.007) increased linearly as the level of supplementation increased. Total VFA concentrations were affected cubically (P = 0.005) by liquid supplementation. Feeding up to 2.27 kg/d of the liquid supplement to steers consuming bermudagrass hay caused a decrease in ruminal pH; however, values were not below 6.0, which is the threshold known to affect fiber digestion. Therefore, we concluded that the inclusion of up to 2.27 kg/d of a 50:50 mixture molasses:crude glycerol in forage based diets fed to growing steers, positively affected ruminal fermentation, increasing propionate concentrations at the expense of acetate, which should improve animal performance.