The objective of the current research was to evaluate the capability of individual rice cultivars to have multi-weed suppressive effects against five currently and potentially important Australian aquatic rice weeds. These weed species are problematic, as resistance occurs to the major herbicide available for their control. Twenty-seven rice cultivars were screened in the laboratory for their allelopathic impact using the Equal Compartment Agar Method against the weeds. Significant differences existed between rice cultivars in their ability to suppress the root growth of each weed studied. Correlations of root inhibition values between combinations of the tested weeds were undertaken to establish rice cultivar inhibition against multiple weed species. All correlations were significant. The highest correlation occurred with Alisma lanceolatum and Sagittaria graminea (r = 0.93), closely related species, and the lowest (r = 0.58) was obtainedwhen comparing Echinochloa crus-galli with S. montevidensis, being unrelated species. The seven most allelopathic cultivars overall inhibited mean weed growth by more than 90%, demonstrating that particular rice cultivars can significantly inhibit multiple weed species.Cluster analysis of the available pedigree information for the tested rice cultivars showed that several rice cultivars with high allelopathic impact in bioassay were grouped in two clusters. This information is useful for plant breeders aiming to incorporate weed allelopathic capability into new crop cultivars.