The present invention relates to an animal and a plant or a by-product thereof having a high content of selenium, and to a method of preparing the same. The present invention relates to a method of increasing the concentration of organic selenium in a plant and an animal (excluding humans) or a by-product thereof, and a plant and an animal and a by-product thereof produced thereby. The method of increasing the concentration of organic selenium in a plant and an animal (excluding humans) or a by-product thereof comprises the following steps: adding inorganic selenium to a medium for culturing microorganisms alone or for mixed culturing； enabling the inorganic selenium to be absorbed by fermentation of the microorganisms so that the inorganic selenium is absorbed into the microorganisms as organic selenium； mixing a microorganism fermentation product having the increased organic selenium with a feed composition, and feeding the mixture to an animal or feeding the microorganism fermentation product to a plant as organic fertilizer； and obtaining the plant and the animal or a byproduct thereof. It has been confirmed that the amount of selenium in an egg produced according to the present invention is increased by more than 185%. The present invention is economical since inorganic selenium relatively inexpensive is used, instead of organic selenium, to increase a content of selenium in a plant and an animal. Such effect may be obtained by using microorganisms which can effectively convert inorganic selenium to organic selenium. The animal and the plant and a by-product thereof having increased selenium, which are produced in accordance with the present invention, are able to implement beneficial functions for the human body such as antioxidant activities and can be used to supply insufficient essential nutrients.본 발명은 고함량의 셀레늄이 함유된 동식물 또는 이의 부산물 및 이의 제조방법에 관한 것으로, 미생물 단독 또는 혼합배양용 배지에 무기 셀레늄을 첨가하는 단계； 상기 미생물의 발효에 의하여 무기 셀레늄이 흡수되어 미생물내 유기 셀레늄으로 흡수되는 단계； 상기 유기 셀레늄이 증가된 미생물
