The atomic layer deposition (ALD) technique has attracted significant attention because it enables the control of film synthesis at the subnanometre scale. Herein, molybdenum oxide (MoO3) ultrathin films using the ALD system through Bis(t-butylimido)bis(dimethylamino)molybdenum (VI) as a molybdenum (Mo) source are prepared. To understand the effect of deposition temperature, thin films are prepared at three different temperatures 100, 150, and 250 °C. The morphological and elemental properties are assessed using a field emission scanning electron microscope, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy techniques. It is observed that the film thicknesses increase with the increase in the deposition temperature. It is found that the film growth at 150 °C is the most potential one for UV optoelectronic applications with high stability even under low applied bias voltages. Moreover, these films show interesting nonlinear optical behaviors as investigated with the z-scan technique applying open and closed aperture methods. The calculated nonlinear optical parameters including nonlinear absorption coefficient (β), nonlinear refractive index (n 2), nonlinear refractive coefficient (γ), and third-order nonlinear susceptibility (χ (3)) are 10−11 m W−1, 10−16 cm2 W−1, 10−11 cm2 W−1, and 10−11 esu, respectively.