Abstract With the assistance of urea, uniform 2D nanoflakes assembled 3D In 2S 3 microflowers were synthesized via a facile hydrothermal method at relative low temperature. The properties of the as-obtained In 2S 3 flowers were characterized by various techniques. In this work, the utilization of urea and l-cysteine, as well as the amount of them played important roles in the formation of In 2S 3 with different nanostructures. Inferred from their morphology evolution, a urea induced precursor-decomposition associated with the Ostwald-ripening mechanism was proposed to interpret these hierarchical structure formation. Furthermore, the optical properties of these In 2S 3 microflowers were investigated via UV–vis absorption and photoluminescence (PL) spectroscopies in detail.