维生素D3(Vitamin D3)，又名胆钙化醇(Cholecalciferol), 是人和动物生长、发育、繁殖、维持生命和保持健康必不可少的一种脂溶性维生素。其主要的生理作用是促进钙磷在肠内的吸收，保证体内钙磷的充分供应，促进骨骼的正常钙化，维持血钙和血磷平衡。临床上用于治疗佝偻病、软骨病和甲状腺机能减退等症。 1α,25-二羟基维生素D3是维生素D的体内代谢产物。25-羟基胆固醇是合成1α,25-二羟基维生素D3（活性维生素D3）的重要原料，之前有人已经成功地用胆酸和岩藻甾醇制备得到了25-羟基胆固醇，且合成的方法步骤比较简单，但是其原料比较贵重，不易得到。 本文重点研究了以相对廉价易得的豆甾醇为原料，制备25-羟基胆固醇的合成方法，经历9步反应得到25-羟基胆固醇，并对实验中得到的中间产品进行了表征。

The Vitamin D3, also known as Cholecalciferol, is a lipid-soluble Vitamin that is essential to person and animals’ pullulation, upgrowth, and propagation, maintaining life and keeping healthy. Its main physiology function is to accelerate the absorption of calcium and phosphor in the intestine, maintain the calcium and phosphor supply well inside the body, promote the normal calcify of the skeleton; keep the calcium and phosphor balance in blood. In clinical application, it is used to cure diseases, such as the rickets disease, the cartilage disease and the thyroid gland function decrease and so on. 1α, 25-dihydroxyvitamin D3 is the metabolic product of vitamin D in body. 25-hydroxycholesterol is the most important raw material to synthesize the 1α, 25-dihydroxyvitamin D3 (active Vitamin D3). Previous studies have shown that the 25-hydroxycholesterol can be synthesized by using cholic acid or fucosterol. However, the starting materials are expensive and not easy obtained. In this thesis, we developed a route to synthesize 25-hydroxycholesterol. By using stigmasterol as the starting material and experiencing nine step reactions, we obtained the target product, 25-hydroxycholesterol with reasonable yield. The product and all the intermediates are examined by 1H NMR, MS.