The mammalian ER/cytosolic α-mannosidase (Man2C1p), yeast vacuolar α-mannosidase (Ams1p) and the Aspergillus nidulans α-mannosidase are members of Class IIC subgroup, which is involved in oligosaccharide catabolism and N-glycan processing. Unlike their mammalian counterparts, the yeast Ams1p and A. nidulans Class IIC α-mannosidase are not essential for morphogenesis and cellular function. In this study, the Afams1, a gene encoding a member of Class IIC α-mannosidases, was identified in the opportunistic pathogen Aspergillus fumigatus. Deletion of the Afams1 led to a severe defect in conidial formation, especially at a higher temperature. In addition, abnormalities of polarity and septation were associated with the ΔAfams1 mutant. Our results showed that the Afams1 gene, in contrast to its homolog in yeast or A. nidulans, was required for morphogenesis and cellular function in A. fumigatus.