Multi-drug resistance is of great concern for public health worldwide and necessitates the search for new antimicrobials from sources such as plants. Several Magnolia (Magnoliaceae) species have been reported to exert antimicrobial effects on sensitive and multidrug-resistant microorganisms. However, the antimicrobial properties of Magnolia dealbata have not been experimentally evaluated. The antimicrobial effects of an ethanol extract of Magnolia dealbata seeds (MDE) and its active compounds honokiol (HK) and magnolol (MG) were tested against the phytopathogen Clavibacter michiganensis subsp. michiganensis and several human multi-drug resistant pathogens using the disk-diffusion assay. The effects of MDE and its active compounds on the viability of human peripheral blood mononuclear cells (PBMC) were evaluated using MTT assay. MDE and its active compounds had antimicrobial activity (inhibition zone > 10 mm) against C. michiganensis, Pseudomonas aeruginosa, Acinetobacter baumannii, Acinetobacter lwoffii, Candida albicans, Candida tropicalis and Trichosporon belgeii. The results suggest that M. dealbata and its active compounds have selective antimicrobial effects against drug-resistant fungal and Gram (-) bacteria and exert minimal toxic effects on human PMBC.