Disclosed is a fluorine-containing oligomer comprising a copolymer of a fluoroalkyl alcohol (meth)acrylic acid derivative of the formula: CnF2n+1(CH2)dOCOCR═CH2 [I], wherein R is a hydrogen atom or a methyl group, n is an integer of 1 to 10, and d is an integer of 1 to 6; and a (meth)acrylic acid derivative of the formula: (CH2═CRCO)mR′ [II], wherein R is a hydrogen atom or a methyl group, m is 1, 2, or 3; and when m is 1, R′ is —OH group, NH2 group that is unsubstituted or mono- or di-substituted with an alkyl group having 1 to 6 carbon atoms, or a monovalent group derived from an alkylene glycol or polyalkylene glycol group containing an alkylene group having 2 or 3 carbon atoms; when m is 2 or 3, R′ is a divalent or trivalent organic group derived from a diol or triol. The copolymerization reaction is performed using a hydrocarbon-based peroxide or azo compound polymerization initiator. Also disclosed are nano-silica composite particles formed as a condensate of the fluorine-containing oligomer and an alkoxysilane with nano-silica particles.