A fluorine-containing copolymer comprising (a) 20 to 80% by mole of the structural unit of the formula:
wherein X is CI or F, (b) 80 to 20% by mole of the structural unit of the formula:
wherein R 1 is an alkylene or alicyclic group, M is an alkali metal or a -NHR 2 R 3 R 4 group in which R 2 , R 3 and R 4 are the same or different and each is H or an alkyl or hydroxyalkyl group, and n is an integer of 2 to 6, (c) 0 to 40% by mole of the structural unit of the formula:
wherein R 5 is an alkyl, alicyclic or fluoroalkyl group, and k is zero or 1, and (d) 0 to 40% by mole of the structural unit of the formula:
wherein n is as defined above, the copolymer being soluble or dispersible in water without using emulsifiers, being capable of crosslinking in the presence of a curing agent and being useful as materials of water-based paints.