To provide a crosslinkable fluorinated aromatic prepolymer which is capable of forming a cured product having a low relative permittivity, high heat resistance, low birefringence and high flexibility, and its uses.A crosslinkable fluorinated aromatic prepolymer which is obtained by subjecting a compound (Y-1) having a crosslinkable functional group (A) and a phenolic hydroxyl group and/or a compound (Y-2) having a crosslinkable functional group (A) and a fluorinated aromatic ring, to a condensation reaction in the presence of a HF-removing agent, with a fluorinated aromatic compound (B) represented by the formula (1): (wherein n is an integer of from 0 to 2, each of a and b which are independent of each other, is an integer of 0 to 3, and each of Rf1 and Rf2 represents a fluorinated alkyl group having at most 8 carbon atoms and a compound (C) having at least 3 phenolic hydroxyl groups, and which has crosslinkable functional groups (A) and ether bonds and has a number average molecular weight of from 1×103 to 5×105.