Corn gluten hydrolysate (CGH) was evaluated in the greenhouse for its herbicidal activity on 19 selected monocotyledonous and dicotyledonous species. Treatments included CGH at 0, 1, 2, 4, and 8 g·dm-2. Plant susceptibility was based on plant survival, shoot length, and root length. The germination and growth of all species were inhibited by the application of CGH at all rates. Black medic (Medicago lupulina L.), buckhorn plaintain (Plantago lanceolata L.), creeping bentgrass (Agrostis palustris Huds.), purslane (Portulaca oleracea L.), and redroot pigweed (Amaranthus retroflexus L.) were the most susceptible species, exhibiting more than 70% reduction in root length, 60% reduction in plant survival, and 52% reduction in shoot length with CGH at 1 g·dm-2. Common lambsquarters (Chenopodium album L.), curly dock (Rumex crispus L.), dandelion (Taraxacum officinale Weber), giant foxtail (Setaria faberi Herrm.), large crabgrass [Digitaria sanguinalis (L.) Scop.], and yellow foxtail [Setaria lutescens (Weigel) Hubb.] exhibited more than 50% reduction in root length and plant survival at 1 g·dm-2. Annual bluegrass (Poa annua L.), barnyardgrass [Echinochloa crusgali (L.) Beauv.], green foxtail [Setaria viridis (L.) Beauv.], orchardgrass (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), quackgrass [Agropyron repens (L.) Beauv.], and velvetleaf (Abutilon theophrasti Medic.) survivial was reduced by 60% at 2 g·dm-2. Annual ryegrass (Lolium multiflorum Lam.) was the least susceptible species.