This document is applicable to fertilizing products, which are classified as PFC 1(A) and PFC 1(B) or the PFC 1(A) and PFC 1(B) component in PFC 7 of Regulation (EU) 2019/1009 [4]. However, the present method was not validated for blends. This document specifies a method for the determination of the biuret content by high-performance liquid chromatography (HPLC) with UV detector. The method is applicable to organic and organo-mineral fertilizers containing urea. Nowadays, there is a method standardized as EN 15479 that allows the determination of biuret in urea by spectrophotometric detection. Organic and organo-mineral fertilizers contain organic matter and other compounds apart from urea that would interfere in a spectrophotometric method. HPLC allows an accurate determination of biuret by separating it from possible interfering compounds [2] [3].