The present invention relates to a vitamin complex composition comprising a green tea extract, a ginkgo leaf extract, a vitamin B group, vitamin C, and ubidecarenone as active ingredients to have an effect of improving a cognitive power and an effect of treating and preventing dementia. The vitamin complex composition comprises a green tea extract containing 300-500 mg of catechin; a ginkgo leaf extract containing 28-36 mg of a flavonol glycoside; 50-100 mg of a vitamin B group; 50-100 mg of vitamin C; and 2.5-10 mg of ubidecarenone.본 발명은 녹차 추출물, 은행잎 추출물, 비타민 B군, 비타민 C 및 유비데카레논을 유효성분으로 포함하고 있음으로써 인지력의 개선 효능과 치매의 치료 및 예방 효능을 가지는 비타민 복합 조성물에 관한 것이다.