Home dental care is a key element of periodontal therapy in veterinary patients. Among many strategies of passive home dental care there is a supplementation of animal diet with seaweed Ascophyllum nodosum which have been shown to reduce both calculus and plaque accumulation after oral administration in both dogs and cats. Ascophyllum nodosum contains numerous biologically active ingredients, including micro-elements, vitamins, and several other compounds, however the exact mechanism of its beneficial action remains unclear. The very first metabolomic data suggest that it could change the composition of dog saliva. Several products containing Ascophyllum nodosum had been assessed clinically according to standards and requirements provided by the Veterinary Oral Health Council. The conducted clinical trials in dogs and cats revealed that Ascophyllum nodosum exerts the strongest preventive action as powder, followed by dental bites and dry pet food. The data concerning its curative action are limited to one study in cats in which no beneficial action has been observed. Based on available clinical data it is recommended to administer Ascophyllum nodosum to dogs and cats after oral cavity prophylactic procedure to reduce the recurrence of plaque and calculus formation.