Thymidine (more precisely called deoxythymidine; can also be labelled deoxyribosylthymine, and thymine deoxyriboside) is a chemical compound, more precisely a pyrimidine deoxynucleoside. Deoxythymidine is the DNA nucleoside T, which pairs with deoxyadenosine (A) in double-stranded DNA. In cell biology it is used to synchronize the cells in S phase. (1) Thymine, along with adenine, guanine, and cytosine, is one of the four nucleic acid bases in DNA; thymine can be used to study chemical processes that affect DNA structure, such as a radiation-induced free radical product resulting in base cross-linking reaction and derivatization reaction. Thymine can be used to study the energy and hydrogen bonding kinetic parameters with other nucleic acid bases such as adenine; thymine is used for the development of (Hg) detectors with sensitive, nanoparticle-based structures and coordination chemistry.

(2)  pyrimidine is an important component of genetic material, is the key intermediates of synthestising anti-AIDS drugs AZT, DDT and related drugs key intermediates, but also the starting material of synthetising anti-tumor, antiviral drug β-thymidine.