The cyclopolymerizations of (2S,5S)-1,2:5,6-diepoxyhexane using BF3 . OEt(2) and tert-BuOK have been studied. The polymer yield and molecular weight of the polymer using tert BuOK were higher than those using BF3 . OEt(2). For the polymers using BF3 . OEt(2), the mole fractions of the cyclized units were 0.76-0.90, and the cyclic constitutional repeating units were five and six-membered rings. The polymer using tert-BuOK essentially consisted of the five-membered cyclic repeating unit.