An HPLC-DAD method was developed for the determination of formaldehyde in animal feed and silage. The method is based on the determination of the product of chemical reaction between formaldehyde and 2,4 dinitrophenylhydrazine. A 3 g of feed or silage were extracted with Milli-Q water with phosphoric acid and next formaldehyde was derivative with the use 2,4 dinitrophenylhydrazine in acetronitrile solution. The extract was purified with 0.45 μm syringe filters and separeted on Zorbax Eclipse XDB C18 column and detection was carried out at 360 nm. Formaldehyde was eluted with a mobile phase consisting of acetonitrile/water in isocratic elution. This method provided average recoveries of 90.6% to 102.2%, with CVs of 2.6% to 6.4% for feed and from 91.3% to 108.7% with CVs of 1.1% to 4.1% for silage in the ranged of 50 to 1000 mg/kg feeds and silage. The LOD and LOQ for formaldehyde in feed and silage ranged from 1.6 to 2.6 and 2.7 to 5.7 mg/kg, respectively. The methodology was applied for the analysis of feed and silage samples collected from poultry, pigs and cows farms.