10-Formyltetrahydrofolate (10-CHO-THF) is a form of tetrahydrofolate that acts as a donor of formyl groups in anabolism.

Two equivalents of 10-CHO-THF are required in purine biosynthesis through the pentose phosphate pathway, where 10-CHO-THF is a substrate for phosphoribosylaminoimidazolecarboxamide formyltransferase.

10-CHO-THF is required for the formylation of methionyl-tRNA formyltransferase to give fMet-tRNA.

The first step generates 5,10-methenyltetrahydrofolate:[2] In the second step 5,10-methenyltetrahydrofolate undergoes hydrolysis: The latter is equivalently written: 10-CHO-THF is also produced by the reaction This reaction is catalyzed by formate-tetrahydrofolate ligase.

It can be converted back into tetrahydrofolate (THF) by formyltetrahydrofolate dehydrogenase or THF and formate by formyltetrahydrofolate deformylase.