The present invention provides a conjugated diene polymer, a method for producing a conjugated diene polymer, a conjugated diene polymer composition and a method for producing a conjugated diene polymer composition. The conjugated diene polymer is a conjugated diene polymer having a conjugated diene-based monomer unit and a group of the formula (I), wherein assuming the whole area of the molecular weight distribution curve obtained by gel permeation chromatography as 100%, the peak area of the molecular weight peak at the lowest molecular weight side is not less than 50%: wherein R1 and R2 represent independently a hydrocarbon group, hydrocarbon oxy group or hydroxyl group, m represents an integer of 0 to 10, and A1 represents a polar functional group free of an active hydrogen atom.