Indium hydroxide, (In(OH)(3)) nanorods and nanocubes were prepared with a precipitation process using a membrane dispersion micronnxer. Indium oxide (In2O3) particles with various sizes were subsequently prepared by calcination of the In(OH)(3) particles. A microreactor was used for its improved mixing performance to obtain. In(OH)(3) particles with a higher degree of crystallinity and In2O3 particles with controllable sizes. The effect of pH, using ammonia as the alkali source, on the In(OH)(3) particle shape and In2O3 particle size with the alkali source of ammonia was investigated. In(OH)(3) nanorods were synthesized at pH = 9.0, whereas at pH = 7.0, In(OH)(3) nanorods and nanocubes were formed. It was observed. that, during the calcination process, the In(OH)(3) nanorods transformed into In2O3 particles with a size Of 20-30 nm, while the In(OH)(3) nanocubes transformed into In2O3 particles with a size of 60-76 nm. It was demonstrated through changing the alkali source that the concentrations of NH4+ and NH3 had a great effect on the morphologies of In(OH)(3), particles during pH values changed by the comparison of different alkali sources. In3+ could be chelated with NH3 to form In(NH3)(4)(3+) which caused In(OH),3 bones to grow faster in one direction than the other directions and resulted in the formation of In(OH)(3) nanorods. However, when chelation with NH3 did not occur, In(OH)(3) nanocubes were formed. Our study explained the effect of pH values and ions concentration on In(OH)(3) particles morphologies and the relationship between In(OH)(3) particle morphologies and In2O3 particle sizes.