In the present work, the effect of different axial non-uniform heat flux profiles on thermo-hydraulic characteristics of natural circulating thermosyphon is investigated numerically. The study has been carried out under steady-state and for open-type thermosyphon. A two-phase flow model has been developed with different heat flux profiles, i.e. linear variation, exponential variation, sinusoidal variation, and uniform variation along the axial length of the riser tubes. The effect of different heat flux profiles is compared under a similar total energy supply. The analysis reveals that the different types of heat flux variations alter the vapor quality distribution, the mass flux, and the onset of tube wall dry-out significantly for different tube diameters.