InSb nanoislands in a GaSb matrix have been fabricated and their structural and luminescence properties have been studied. The deposition of ∼1.7 monolayers of InSb in a GaSb(100) matrix has been found by transmission electron microscopy to result in a 2D-3D growth mode transition and a formation of small InSb quantum dots (QDs) with lateral sizes of-10 nm. Bright luminescence due to these QDs is observed. Stacking of the QDs results in a formation of vertical-coupled QD planes and leads to a long wavelength shift of photoluminescence line associated with the QDs. Increase in the InSb layer thickness above ∼2 monolayers results in formation of 3D dislocated InSb islands with a lateral size above 60 nm and the dramatic drop of photoluminescence intensity.