The paper presents the characterization of the content of metals from three different waste biomass using ICP-MS and AAS techniques. The purpose of the study was to finding an appropriate method of analysis for the complex matrix of waste biomass by comparing two methods of digestion using a closed system (microwave) and an open system (sand bath). For this study were analyzed six metals (Al, Mg, K, Ca, Na, Fe) in three different waste samples from agriculture, forestry and related industries (horticultural and wine waste). It was observed that the highest concentrations of metals were recorded for the sample P3 horticultural and wine waste through both analysis techniques. The results obtained were compared with a certified reference material (CRM) and value to demonstrate the precision of the method and the quality of the results. The concentration obtained for Al, Mg, K, Ca, Na and Fe by microwave digestion in a closed system analyzed using ICP-MS technique were better than the AAS technique. The method of analysis chosen in this study was emphasized as being optimal for the analysis of biomass waste using performance parameters: precision, accuracy, detection limit, quantification limit and extended uncertainty. From the obtained results it can be said that the method of digestion by using microwave systems of the metals` analysis from biomass waste is within the desired purpose.