The present invention provides a diene polymer in which a polar functional group is introduced into an end by radical polymerization, and its production method; a polymer emulsion and a rubber composition each containing the diene polymer; and a pneumatic tire containing the rubber composition. The present invention relates to a diene polymer, which is obtained by radical polymerization of at least one radical polymerizable monomer in the presence of at least one polar functional group-containing thiol compound, and has a polar functional group at at least one end: The polar functional group-containing thiol compound is preferably represented by formula (1): X—R1—SH  (1) wherein X represents an ester group, a hydroxyl group, a carboxyl group, an amino group, or an alkoxysilyl group, and R1 represents an alkylene or arylene group which may have a substituent.