桐油是取自大戟科油桐属树木油桐种子的油，在空气中氧化经聚合反应生成致密的漆膜。和其他干性油比有干燥快、比重小、附着力强、耐热、酸、碱等优点。

桐油原产中国，传统上用来涂抹保护木器、制造油布、油纸等防水材料，调制油泥镶嵌缝隙，中医用来调和膏药等外用药。桐油在现代用于做木器油漆、油墨、制造合成树脂等。

中国传统的桐油来自三年桐（Aleurites fordii Hemsi.）和木油桐（Vernicia montana，又名千年桐）。日本油桐（Aleurites cordata Thunb.）所产的油称为日本桐油。 油桐种子含油率一般在35％以上，其中种仁含油率60％左右。成熟的种子采收后，去除果皮和种皮，用压榨的方法榨油，剩余的麸饼还可以进一步用溶剂萃取。这样制得的生桐油外观淡黄、暗红或暗黑色，分别称为白／红／黑桐油。生桐油干燥速度较慢，而且漆膜的透明性和粘性较差。生桐油加一氧化铅等进一步熬制成为熟桐油，又称光油，更加适合做涂料。

Tung oil or China wood oil is a drying oil obtained by pressing the seed from the nut of the tung tree (Vernicia fordii). Tung oil hardens upon exposure to air, and the resulting coating is transparent and plastic-like, a property exploited in most of its applications, such as wood finishing, as well as the composition of oil paints and printing inks. Related drying oils include linseed, safflower, poppy and soybean oils. The oil and its use are believed to have originated in ancient China and appear in the writings of Confucius from about 400 B.C. Raw tung oil tends to dry to a fine wrinkled finish; the US name for this is gas checking: this property was used to make wrinkle finishes, usually by adding excess cobalt drier. To stop this, the oil is heated to gas-proof it, and most oils used for coating are gas-proofed.