Process for the preparation of C4-C6 alkenes with terminal double bound

4-6C alkenes with internal double bonds are obtained from 4-6C alkenes with terminal double bonds by a hydro-isomerisation process in which part of the product stream is returned to the reactor. A process for the production of 4-6C alkenes with internal double bonds (I) by hydro- isomerisation of 4-6C alkenes with terminal double bonds (II) comprises (a) introducing a feed comprising alkenes (II), hydrogen and a return stream with a temperature of 15-60 degrees C into a reactor packed with a Group VIII precious metal- containing catalyst, (b) isomerising (II) with an LHSV of 1-20 h at 15-120 degrees C and at a pressure such that (II) is in the liquid phase, and essentially establishing thermodynamic equilibrium between (II) and (I), (c) splitting the product stream into a work-up stream (A) and a return stream (B) comprising 0.1-10 times the amount of (A) in the steady state, and (d) recycling stream (B) to stage (a) and (e) isolating (I) from stream (A).