Abstract: Objective: The present study was conducted to determine the dosage effects of Saccharomyces spp. Kb-5 (isolated from buffalo rumen fluid) as a probiotic on egg production performance, egg quality characteristics and mineral and cholesterol concentrations in the yolks of eggs from laying ducks. Materials and Methods: Two hundred and forty 40-week-old healthy laying ducks (Anas sp.) were used in a completely randomized design divided into four treatment groups: S0, without administration of the probiotic; S1, with administration of 0.10% Saccharomyces spp. Kb-5; S2, with administration of 0.20% Saccharomyces spp. Kb-5 and S3, with administration of 0.30% Saccharomyces spp. Kb-5. Results: This study showed that administration of Saccharomyces spp. Kb-5 increased egg mass, feed efficiency, feed digestibility, yolk color, yolk and eggshell weight, shell thickness and Ca content in the eggshell and yolk (p<0.05) but did not increase the efficiency of feed consumption (p>0.05). Administration of 0.20-0.30% Saccharomyces spp. resulted in lower (p<0.05) yolk cholesterol contents. Conclusion: It is concluded that supplementation of laying duck diets with 0.20-0.30% Saccharomyces spp. Kb-5 increased egg mass, feed efficiency, feed digestibility, yolk color, yolk and eggshell weight, shell thickness and Ca contents in the eggshell but decreased yolk cholesterol contents.