Chemical and microbiological characteristics of compost and vermicompost are very similar. However, crop response to vermicompost application is often higher than to conventional compost application. With the purpose to evaluate the quality and the differences between these two kinds of compost, the C-organic and N-total dynamics were analyzed, and their relationship with microorganisms during composting and vermicomposting of grassyard clippings mixed with rabbit manure (3:1 v/v) were studied. The substrate was deposited in wooden containers and the factors above mentioned were evaluated every four weeks. The pH (8.5) and electrical conductivity (8 dS m ‐1), reached by the substrate during its transformation, were harmful to earthworms and microorganisms. The increase in pH diminished N-total concentration; for this reason, the C/N ratio did not change during the process. The largest N loss was observed in vermicompost, in its production there was a stronger relationship between N-total and N-fixing microorganisms (R2=0.96) than in compost (R2=0.57). In the organic residue, transformation of C-organic content was diminished to 29% after 16 weeks. Microbial respiration was highly correlated with the C-organic during the composting process (R 2 =0.97) and less in the vermicomposting process (R 2 =0.80). The population of bacteria decreased during the process, and had a positive association with microbial respiration (R 2 =0.75 and 0.82 during composting and vermicomposting, respectively). However, the changes observed in fungal populations did not show a specific tendency, maybe because fungi prefer slightly acid conditions. These results show that alkalinity and salinity have a negative effect on earthworms and microorganism populations.