The study aimed to develop some methods for the compositional characterization of biodegradable waste with relevance to the composting process at the laboratory level. For testing, four waste fractions were selected, such as waste based on dehydrated sludge, waste from parks (leaves, branches), market waste (mixture of vegetable and fruit) and cardboard waste. For metals and phosphorus, several microwave digestion methods were applied. The ammonium nitrogen content (NH4-N) was determined using a number of extraction procedures (water, CaCl2, and KCl). Three certified reference materials were used for testing the validity of the results. Recovery percentages higher than 90% were obtained. The developed and validated methods are suitable for biodegradable waste characterization used in composting processes.