Honeycomb-structured microporous films were self-assembled from a new type of multiarm copolymer, hyperbranched poly(3-ethyl-3-oxetanemethanol)-star-polystyrene (HBPO-star-PS). The precursor consisting of an HBPO core and a number of PS arms was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The microporous film was prepared by the evaporation of a chloroform solution of the precursor in a humid atmosphere (the so-called breath figure method). Compared to our former work, the hexagonally packed pores in the film were not interpenetrated and isolated from one another by the walls. The size of the pores could be controlled easily by changing the casting volume of the solution, the molecular weight and concentration of the polymer, and so forth. The water contact angle on the film surface indicated that the hydrophobicity of the film surface was significantly enhanced as a result of the formation of the porous structure.