In the study, an efficient process was proposed to prepare ALD MnOx films with bis(N,N'-di-tert-butylacetamidinato)manganese-(II) (Mn(Bu-t-MeAMD)(2)) and H2O. The process follows ideal self-limiting growth behaviors. The as-prepared smooth and pure MnOx films with a high growth rate of similar to 2.1 angstrom/cycle were characterized by SEM, AFM, XRD and XPS methods. The MnOx films could conformally and uniformly grow into deep narrow trenches with high aspect ratios of 10:1, highlighting the application potential of the ALD process in complex 3D or porous structures-based nanoengineering.