Mycotoxins, secondary metabolites of toxigenic fungi, affect animal and human health worldwide. Two mycotoxins commonly found in dairy rations are the Fusarium mycotoxins deoxynivalenol (DON) and fumonisins (FUM). Under field conditions, it has been shown previously that milk of dairy cows exposed to mycotoxins had a significantly lower curd quality and curd firmness in comparison to cows not exposed to mycotoxins. The aim of this trial was to investigate the effect of DON and FUM in the feed on milk quality and rennet coagulation properties of dairy cows. A feeding trial was conducted using 12 Holstein cows in a randomized block design. Cows received either (1) a control diet (CTR), (2) a TRM contaminated with Fusarium mycotoxins (0.4 mg/kg DON and 1.1 mg/kg FUM) (MTX), or (3) the contaminated TRM supplemented with a mycotoxin deactivator (MD) (35 g/animal/day) (MTX+MD). The contamination level was lower than the recommended maximum values for dairy feed in Europe (5 mg/kg DON and 50 mg/kg FUM) and represent contamination levels that can be commonly detected in dairy rations. Each of the 3 experimental periods consisted of a 3-week treatment period followed by a 2-week clearance period. Individual milk samples were taken once a week for determination of coagulation properties (curd firming time k20 in minutes and curd firmness a30 in mm). The GLM (General Linear Model) procedure of SAS (SAS 9.4 TS, 2018) was used and LSMeans were compared post-hoc. The treatments had no significant effect on casein content, titrable acidity and clotting time of the milk. The mycotoxin diet showed however significant negative effects on curd firmness (a30) as well as curd firming time (k20) and in both parameters the addition of MD alleviated these negative effects (a30: CTR: 30.44 mm; MTX: 25.06 mm; MTX+MD: 32.44 mm; P < 0.05, k20: CTR: 8.07 min; MTX: 13.0 min; MTX+MD: 9.71 min; P = 0.05). In conclusion, dietary concentrations of FUM and DON commonly detected in dairy rations had a negative effect on milk rennet coagulation properties. The MD counteracted these negative effects.