A new anaerobic rumen fungus was isolated from the rumen fluid of a yellow cow (Bos indicus). This fungus appears to be a previously undescribed species of the genus Caecomyces, it possessing uniflagellate zoospores, a spherical holdfast, tubular sporangiophores and bulbous rhizoids. This new fungus also features distinctive multisporangiate thallus sympodially distributed on sporangiophores. The fungus resembles Caecomyces communisand C. equiin that it characterizes bulbous rhizoids and uniflagellate zoospores but differs from C. communisand C. equiin that it possesses multisporangiate and sympodial sporangia. This new fungus and Cyllamyces aberensisboth reveal similar morphology during early thallus development in having a spherical holdfast, but they vary from unbranched sporangiophores and additional bulbous rhizoids. In addition, the molecular phylogenetic analyses ITS1 (internal transcribed spacer 1) also conform to the results of the morphological examinations of Caecomyces. For the mentioned reasons, this new species of fungus is described as Caecomyces sympodialissp. nov. The genera of Neocallimasticaceae and species of Caecomycesare also keyed out.