Protein arginine methylation has been implicated in different cellular processes including transcriptional regulation by the modification of histone proteins. Here we demonstrate significant in vitro activities and multifaceted specificities of Aspergillus protein arginine methyltransferases (PRMTs) and we provide evidence for a role of protein methylation in mechanisms of oxidative stress response. We have isolated all three Aspergillus PRMTs from fungal extracts and could assign significant histone specificity to RmtA and RmtC. In addition, both enzymes were able to methylate several non-histone proteins in chromatographic fractions. For endogenous RmtB a remarkable change in its substrate specificity compared to the recombinant enzyme form could be obtained. Phenotypic analysis of mutant strains revealed that growth of DeltarmtA and DeltarmtC strains was significantly reduced under conditions of oxidative stress. Moreover, mycelia of DeltarmtC mutants showed a significant retardation of growth under elevated temperatures.