This report describes the results of the research into the effect of anaerobic digestion on the orthophosphate content in dairy manure. On different dairy farms with a manure digester and separators samples were taken from the manure, digestate, liquid fraction, thick fraction and analyzed on the content of orthophosphate. Furthermore, the orthophosphate was extracted from the liquid fraction with calcium hydroxide. The orthophosphate content decreases as a result of anaerobic digestion. The orthophosphate content was on average 34 mg/kg in the digestate and was lower than in the incoming manure with average content of 75 mg/kg.