We theoretically studied size-dependent emission properties and intersubband (ISB) transitions in cubic InN (c-InN) quantum dots (QDs) and In-rich c-InGaN clusters. The quantum size effect can affect the energy levels and emission properties of such nano-structures, depending on composition, size, effective mass, and strain. In small c-InN QDs and In-rich c-InGaN clusters, strong quantum size effect enhances size-dependent emission properties and leads to fewer eigen-states. In larger c-InN QDs and In-rich InGaN clusters, ISB transitions between eigen-states of the conduction band can be applied in telecommunication devices. By varying the sizes of nano-structures, we can control the largest ISB transition energy difference between the ground state and the highest confined eigen-state. Simulation results also show that ISB absorption wavelengths can be altered by changing the composition and size of nano-structures. (c) 2008 Elsevier B.V. All rights reserved.