The understanding of the transformation mechanism involved in the dehydroxylation reactions in the In–O–H system exhibits large controversy and discrepancy; it holds especially for the formation of the metastable nanosized intermediates as well as for the structural relation between corresponding phases. It was recently reported that indium oxohydroxide (InOOH) appears as an intermediate phase in the thermal dehydroxylation of nanoscaled In(OH)₃. Our in situ time resolved high energy synchrotron radiation experiments showed unambiguously that no intermediate crystalline or amorphous phases have been observed during the phase transition (dehydroxylation) from nanosized indium hydroxide to indium oxide. Under our experimental conditions, the c-In(OH)₃ to bixbyite-type In₂O₃ transition was observed between 280 and 305 °C and the conversion completed around 305 °C without any observable intermediates. The formation of InOOH during the phase transition  In₂O₃ can be ruled out. This finding is of high relevance and importance for the controllable synthesis of nanocrystalline In₂O₃-based materials.