A heap of farm yard manure (2 x 2 x 1.5 m height) was stored for l00 days. Periodical samples were collected from the heap after initial, 2, 4, 6, 8, 10 and 12 weeks for isolation of some thermophilic actinomycetes, and determination of their enzymatic activities to decompose cellulose by the determination of C₁ & C_x cellulases. The counts of total bacteria, spore formers, aerobic cellulose decomposing bacteria, fungi, mesophilic actinomycetes and thermophilic actinomycetes were carried out. The recorded temperature of the heap at the depth of 60-40 cm was 70^oC after 4 weeks from the beginning of the storage. The pH showed continuous decreases from 8.2 to 6.5 at the end of the experiment.                 The microbiological studies of the collected samples showed higher counts of total bacteria then decreased till the end of the experiment. The spore formers reached the highest counts after 4 – 5 weeks then decreased. The counts of aerobic cellulase decomposing bacteria reached maximum after 6 weeks then decreased to the end of the experiment, as well as the counts of fungi has the same pattern. The mesophilic actinomycetes showed higher counts at the beginning of the storage then decreased on the expense of the thermophilic actinomycetes, which greatly increased by increasing of heap temperature; reached maximum after 4 – 6 weeks; while the mesophiles diminished.                 Sixty isolates of thermophilic actinomycetes were isolated from the heap for purification and identification these isolates were identified according to Bergey's manual (1998) were related to 5 species of them 3 genera which were highly active namely. Thermoactinomyces, Thermomonospora and streptomyces respectively. The enzymatic activity of these strains showed high activity of C₁ and Cx cellulases. The highest active Thermoactinomyces saccharia, thermoactinomyces vulgaris, Thermomonospora fusca, Thermomospora alba and Streptomyces thermofuscus.