The functional protein microarray is a powerful and versatile systems biology and proteomics tool that allows the rapid activity profiling of thousands of proteins in parallel. We have recently developed a human proteome array, the HuProt array, which includes ~80 % of all the full-length proteins of the human proteome. In one recent application of the HuProt array, we identified numerous SUMO E3 ligase-dependent SUMOylation substrates. For many SUMO E3 ligases, only a small number of substrates have been identified and the target specificities of these ligases therefore remain poorly defined. In this protocol, we outline a method we developed using the HuProt array to screen the human proteome to identify novel SUMO E3 ligase substrates recognized by specific E3 ligases.