The present invention provides a preparation method of fermented onion extract for resisting lung, liver and prostate cancer resistance. In which, the onion raw material is placed in a fermentation environment at temperature of 55 or 75 DEG C and relative humidity of 40% for fermentation for 7 to 28 days to obtain black onions； then, extracting the fermented onion extract from the black onions. The fermented onion extract prepared by the present invention is confirmed by experiments for having the ability to effectively inhibit the growth of cells of lung, liver and prostate cancer.一種用於抗肺癌、抗肝癌及抗前列腺癌之發酵洋蔥萃取物製法，主要係將洋蔥原料置於溫度55℃或75℃及相對濕度40%之發酵環境下，發酵7~28天以製得黑洋蔥後，再由該黑洋蔥中萃取出發酵洋蔥萃取物。而本發明所製得之發酵洋蔥萃取物經試驗後證實具有可有效抑制肺癌、肝癌及前列腺癌細胞生長之能力。
