PURPOSE: A microbial composition to be added to feedstuff as a feed additive and a preparation method thereof are provided to improve the color of an egg yolk by increasing xanthophyll content in the egg yolk. CONSTITUTION: A method for preparing a microbial composition to be added to feedstuff as a feed additive comprises the following steps of: extracting xanthophyll content including lutein from marigold bloom through alcohol fermentation for up to 24 hours; separating the extract into a solid portion and liquid portion using Kimchi lactobacillus such as Latobacilus plantarum; concentrating the liquid portion in a concentrator and mixing the solid portion, concentrate, and excipient; drying the mixture; and adding the obtained microbial composition by 0.1-0.2% of the feedstuff.