Composting evolution of two different agave bagasse provided by two tequila factories was monitored at 0, 28, 56, 84, 112 and 126 days using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) to assess their degree of decomposition. Stages of decomposition were assessed using their IR spectral pattern since the characteristic bands undergo changes during the biological treatment of the agave bagasse. Additionally, the samples were analyzed using the temperature range from 40 to 600 ºC in nitrogen atmosphere in order to assess the changes. Agave bagasses (without composting) had the higher mass loss percentage in TGA and these losses diminished as the composting process progressed. The DTG curves showed two peaks which can be attributed to the degradation of the hemicelluloses and cellulose. Scanning electronic microscope observations showed significant changes in the structure of the vascular bundle in agave bagasse samples after 126 days of composting and massive fungal invasion that led to the cracking of the fiber. Weakening the structure of the vascular bundles of the agave bagasse by composting can improve water retention capacity of bagasse that is to be used as a substrate for greenhouse vegetable production.