Butene oligomer derivatives having tert-butyl groups as one of the terminal groups, having a repeating unit of the main hydrocarbon chain consisting of 80% by mole or more of nullCH2C(CH3)2null, and carrying the other terminal group consisting of 60% by mole or more of 1,4-butanediol type functional groups. These derivatives are useful as macromonomers which can be subjected to polycondensation, polyaddition, etc.