Although grassland has a significant biomass potential, many different factors can affect the quality of grassland feedstock. Changes in the chemical composition of grassland biomass can lead to a high variation-in biogas potential, even within the same plant species. Therefore, four grass species and two legume species were grown infield plots and harvested at sequential stages of maturity in the first three growths. The samples were investigated in order to mathematically describe the relation between their chemical composition and biogas yield. A global biogas yield prediction model for energy Crops allowed the differentiation between the samples for biogas yield. However, due to their distinct difference in plant chemical Composition, the estimation accuracy was rather low. A model considering lignin, hemicellulose, and crude protein as regressors was most suitable for predicting the biogas yield of grassland plant species, with an accuracy of 31 L/kg volatile solids.