Contents of water stable aggregate in the casts were related to the microbial properties. The water stable aggregates and the microbial properties of earthworm casts were both changed with ageing time and the nature of organic matter. However, few studies were carried out in this area. This study reported some results from a short term laboratory experiment. The aims were to study the effects of aging, drying and different organic matter on microbial properties and the stability of structure in worm casts. Endogeic earthworms (Metaphire guillelmi), maize residues and cattle manure were used in the experiment. The four treatments were: (1) OM one day casts with maize residues; (2) AM aging casts with maize residues; (3) OC one day casts with cattle manure and 4) AC aging casts with cattle manure. Fresh and air dried casts were both analyzed also. Results showed that the aging process decreased the microbial biomass carbon, the number of fungi and the basic respiration rate in the treatments AM and AC. The number of bacteria in the treatments with cattle manure was greater than the treatments with maize residues, but the number of fungi was less than that. Ageing increased the content of the total water stable aggregates (> 0.053 mm), especially of the large macro aggregates (>2mm). Significant differences were observed between the treatment of OM and AM. Drying increased the total content of water stable aggregates and part of them concentrating to micro-aggregates having stronger stability. The organic matter application did not show effects on total water stable aggregates in fresh casts. The content of water stable aggregates(0.25-0053mm) in the treatments with maize residues was significant greater than the treatments with cattle manure, but was significant lower than the treatment with cattle manure after air drying treatment. In air dried casts, the number of fungi, the SMBC and the basic respiration rate were positively related to the content of large macro aggregates. However, in fresh casts only the number of bacteria was positively correlated with the content of large macro aggregates.