Abstract: The behaviour of crystalline phase separation in soft and hard blocks greatly influences the transparence and mechanical properties of polyurethanes. By using dicyclohexylmethane diisocyanate, poly(propylene oxide) and 1,3-butylene glycol, the flexible transparent polyurethanes were synthesized that is fully amorphous. When the hard segment content is 47% (wt), they show very good transparence and mechanical properties with transparency 93%, tensile strength 18 MPa, elongation at break 358%, Shao-A hardness 90 and non-yellowing after a time.