Ellagic acid (EA) could be converted into urolithins to exert health-promoting effects by intestinal flora, but the biotransformation capacity varied among individuals. Strategies targeted on gut microflora modulation could be a novel method to obtain more urolithins beyond the inter-individual variability. The study aimed at investigating the impacts of four algal polysaccharides (APs) supplements on EA biotransformation. Results showed that simple APs supplements would increase certain urolithin productions, and APs-EA solid dispersions supplement improved urolithins contents from 4.25 μmol to 6.16-6.79 μmol. The enhancement was related to the proliferation of the EA-metabolic-related bacteria like Gordonibacter, Faecalibacterium, Sutterella, Dialister, Enterocloster and etc. and increasing the bioaccessibility of EA to the bacteria. Furthermore, mono-/co-culture fermentation further verified that Gordonibacter urolithinfaciens was greatly proliferated by simple APs and EA solid dispersions supplements. EA/UPP 1-1 showed the best performances in urolithins productions, and the total urolithins contents increased by 3.78 times compared to control EA group. These results showed dietary supplements could improve biotransformation ability by influencing the EA-metabolic-related bacteria and the access to substrates.