Abstract: There is provided a process for producing ultrafine particles by preparing one or more than one kind of alkoxide of a metal which is a component of the desired ultrafine particles, and subsequently hydrolyzing or heating said alkoxide. For the production of ultrafine particles of ruthenium oxide and/or metallic ruthenium, which are used as a raw material of thick film resistors, a ruthenium compound is reacted with an alkali metal alkoxide to give a ruthenium alkoxide and it is hydrolyzed or heated. For the production of a low-melting glass (including lead oxide), which is used as a sintering assistant or easy-to-sinter powder, at least three kinds of compounds (alkoxides or sols) including a lead alkoxide are reacted with one another and the resulting reaction product is hydrolyzed.