Protein ubiquitination, an evolutionarily conserved post-translational modification process in eukaryotes, and plays an important role in many biological processes. Aspergillus nidulans, a model filamentous fungus, contributes to our understanding of cellular physiology, metabolism and genetics, but its ubiquitination remains widely unknown. In this study, the ubiquitination sites in the proteome of A. nidulans were identified using a highly sensitive mass spectrometry combined with immuno-affinity enrichment of ubiquitinated peptides. The 4816 ubiquitination sites were identified in 1913 ubiquitinated proteins, accounting for 18.1% of total proteins in A. nidulans. Bioinformatic analysis suggested that the ubiquitinated proteins are associated with a number of biological functions and display various sub-cellular localizations. Meanwhile, seven motifs were revealed from the ubiquitinated peptides, and significantly over-presented in different pathways. This study presents a first proteome-wide view of ubiquitination in filamentous fungi, and provides an initial framework for exploring the physiological role of lysine ubiquitination in filamentous fungi.