Abstract: A process for the preparation of transparent polyurethanes is disclosed, comprising step a) of preparing a prepolymer by reaction of one or more aliphatic or cycloaliphatic isocyanates, having two or more isocyanate groups, and one or more polyhydroxy compounds, having two or more hydroxy groups and a molecular weight ranging from 150 to 2000, step b) of preparing a composition comprising one or more polyhydroxy compounds, having two or more hydroxy groups and a molecular weight ranging from 150 to 2000 and a functionality from 2 to 5, and a suitable catalyst, and step c) of reacting the so-obtained prepolymer with the composition of step b), wherein at the end of step a) the percentage of free isocyanate groups in the prepolymer is at least 15%. In the preferred disclosed process, the percentage of free isocyanate groups in the prepolymer is from 15 to 30%. Particularly, a composition for the preparation of transparent polyurethanes and polyurethanes obtainable by said process are disclosed.