Quantitative determination of enzyme activities can be used to evaluate the dynamics of the composting process. An enzyme activity assay in solid phase was developed in which the enzyme reaction is performed by mixing the compost sample and the corresponding substrate with a water content equivalent to the water retention capacity (WRC) of the compost sample. As opposed to common activity assays that extract and quantify soluble enzymes, this solid phase method evaluates total enzyme activities under conditions closer to those found in the actual composting process. Preliminary results on enzyme activities of a compost of poultry manure and sawdust include amylase, invertase, cellulase, phosphatase, protease, and dehydrogenase activities. With the exception of proteases, all increased from day 9 to 43 of the composting process.