Atomic layer deposition (ALD) using (MeCp)PtMe3 and O2 gas or O2 plasma is a well-established technique for the deposition of thin films of Pt, but the potential of ALD to deposit platinum oxide (PtOx) has not yet been systematically explored. This work demonstrates how PtOx can be deposited by plasma-assisted (PA)-ALD in a temperature window from room temperature (RT) to 300 °C by controlling the O2 plasma and (MeCp)PtMe3 exposure. With increasing substrate temperature, the thermal stability of PtOx decreases and the reducing activity of the precursor ligands increases. Therefore, longer O2 plasma exposures and/or lower (MeCp)PtMe3 exposures are required to obtain PtOx at higher temperatures. Furthermore, it is established that, during the nucleation stage, PtOx ALD starts by the formation of islands that grow and coalesce during the initial ∼40 cycles. Closed-layer thin films of PtOx with an O/Pt ratio of 2.5 can be deposited at 100 °C with a minimal thickness of only ∼2 nm. It is also demonstrated that a conformality of ∼90% can be reached for PtOx films in trenches with an aspect ratio of 9 when using optimized O2 plasma and precursor exposure times.