Objectives were to evaluate the effects of calcium nitrate (CN) feed for dairy cows on dry matter intake (DMI), milk yield, milk composition, and ruminal fermentation parameters. The hypothesis was that CN could be feed for dairy cows without affecting rumen fermentation parameters and milk composition. Six multiparous lactating dairy cows (106.3 ± 14.8 d in milk; 550.7 ± 21.8 kg-body weight; mean ± SD) were enrolled in a replicated 3 × 3 Latin square, each period was 21 d, with 14 of adaptation and 7 d of collection. Cows were fed ad libitum a TMR composed of 53% corn silage and 47% concentrate on dry matter (DM) basis. The diets were formulated to meet the NRC requirements for a 600 kg Holstein cow in mid-lactation, the diets were isocaloric and isonitrogenous with 16% of crude protein and 11% of rumen degradable protein, nitrogen content was manipulated by adding CN (66.9% NO₃^-). Treatments were: T1: a diet without CN; T2: a diet with 1.5% CN on DM basis; T3: a diet with 3% of CN on DM basis. Milk samples were collected on d 15–16 of each period and analyzed for milk components. Ruminal fluid was collected 2 and 8 h after feeding the pH was determined, and the volatile fatty acids (VFA) profile was determined by gas chromatography. Data were analyzed by ANOVA with mixed models using the Mixed procedure in SAS. DMI and milk true protein were reduced (P < 0.05) by T3. However, the treatments had no effect on milk yield (P > 0.10). There was a tendency (P = 0.09) to decrease energy-corrected milk (ECM) and fat corrected milk (FCM). Lactose and milk urea nitrogen did not differ between treatments. The concentration of isovaleric had a linear reduction (P < 0.04) with the increase of CN in the diet, there was a tendency (P = 0.06) to increase the acetate:proprionate ratio. The results demonstrate that CN reduces milk true protein and tended to reduce ECM and FCM, however milk efficiency was not affected by feeding CN. Calcium nitrate can be used up to 1,5% of DM basis on dairy cows in corn-based diets without affecting milk composition and without affecting the rumen fermentation parameters.