A modified diene polymer is provided which may be added to a rubber composition together with a filler to allow the filler to be dispersed in a crosslinked product of the composition in a state that is ideal for attaining enhanced properties. A method for producing such modified diene polymers is also provided. The modified linear diene polymer has a specific functional group only at one end thereof, the average number of the functional groups per molecule being 0.8 to 1.