In this article, pure and 2 M% dysprosium (Dy)-doped α-MoO3 nanobelts have been successfully synthesised by the autoclave assisted-hydrothermal method. The x-ray diffraction (XRD) patterns revealed that the nanobelts were crystalline in nature with an orthorhombic structure. The sharp and narrow XRD peaks divulged the high quality with good crystallinity of the nanobelts. The intensity of the peak (040) increased and shifted towards lower 2θ values which reflected the successful incorporation of Dy in MoO3 matrix. The scanning electron microscopy (SEM) images revealed the formation of randomly distributed nanobelts with average width of 90–150 nm and length of 950–1300 nm. Vibration behaviour of chemical bonds was characterised by Fourier-transform infrared spectroscopy (FTIR) and the detected peaks confirm the formation of orthorhombic structure of MoO3. The energy dispersive x-ray spectroscopy (EDX) spectra confirmed the Dy incorporation in the MoO3 matrix. Debye–Scherrer method, Wilson method, Williamson Hall (W − H) and Halder-Wagner (H − W) analyses have been employed to investigate the different parameters (such as crystallite size and lattice strain) and to analyse their contribution on the XRD peak broadening of the nanobelts. The crystallinity improved as the average crystallite size increased, and FWHM, lattice strain and dislocation density decreased after Dy doping. The obtained values of crystallite size estimated using Debye–Scherrer equation, and W − H and H − W plots, are nearly similar, highly inter-correlated and in the range of 26.06–31.44 nm. The Halder-Wagner (H-W) plots give the more precise results of different microstructural parameters by analysing XRD peak broadening of both samples compared to Debye–Scherrer and Williamson Hall methods.