Poly(trimethylene carbonate) (PTrMC) is a member of poly(alkylene carbonate) represented by the chemical formula [-(CH2)(m)OC=OO-](n). PTrMC is found to be a synthetic rubber, which is amorphous in the relaxed state and crystalline in the stretched state. PTrMC can be synthesized enzymatically and therefore can be called a biodegradable elastomer. In the present study, the crystal structure analysis of PTrMC was carried out using an imaging plate by the X-ray diffraction method. Two molecular chains pass through a unit cell with parameters a = 7.02 Angstrom, b = 5.81 Angstrom, and c(fiber axis) = 12.30 Angstrom and the space group P2(1)cn-C-2v(9). The molecules assume the (S) over bar TST(2)GST (S) over barT(2)(G) over bar conformation distorted from T(5)GT5 (G) over bar.