The results on fabrication of refractive microlens arrays using heat forming and reactive ion beam etching (RIBE) techniques are presented. RIBE, with high etching rate and flexible etching ability, is a novel dry etching technique for manufacturing micro optical element. The principle of the method and the controlling of etching selectivity are described. In experimetns, we have fabricated F/2 microlens array with 100 μm diameter in the surface of silicon. An accurate control of etching rate ratio between positive photoresist and silicon was obtained by adjusting multiple etching parameters. The measurement of microlenses showed that the lenslet profile was very close to the standard spherical surface profile. The duplicating ratio is 1:1.03.