The invention relates to a preparation method of a purified extract of natural allergens. The preparation method comprises following steps: (a) extracting a natural source of allergens comprising allergenic proteins to form an extract (b) purifying the extract to remove non-protein components to form the purified extract (c) denaturating the purified extract to form a purified denaturated extract which comprises protein, wherein the most abundant (w/w) proteins forming together at least 60% (w/w) of all proteins are at least two proteins, and the all proteins represent at least 60% (w/w) of the dry weight of the purified denaturated extract. The invention also relates to a preparation method of a purified extract of natural allergens. The preparation method comprises following steps: (a) hydrolyzing a denaturated allergen to form an allergen hydrolysate (b) purifying the allergen hydrolysate to remove peptides with a molecular weight above 10,000 Da and below 1,000 Da so as to obtain a purified hydrolysate, wherein 70%, more preferably 80% of the peptides are between 10,000 Da and 1,000 Da.
