Saprophytic fungi are one of the most active decomposers of forest litter, and their diversity may be influenced by the spatial heterogeneity of substrates. We examined the changes in saprophytic community structure and composition across a volcanic soil chronosequence, at Sierra del Chichinautzin, Mexico. Saprophytic fungi were collected for three consecutive years at three sampling sites with contrasting soil properties in a volcanic soil chronosequence ranging from 1,835 years B.P. to 10,000 years B.P. Although no significant differences were found in terms of abundance and richness between the three sites, Shannon diversity was higher at the youngest, less-fertile site. The high percentage of site-exclusive species showed that species composition was strongly dependent on the site and therefore on soil parameters. Different saprophytic species had divergent responses to soil variables, but most fungal taxa correlated negatively with the edaphic factors we measured. The highest diversity found at the young, less fertile site may represent an "insurance" mechanism against harsh conditions, since different species are likely to play various ecological functions which may lead to a more efficient degradation of recalcitrant substrates.