Abstract: An experimental investigation was performed on the density wave oscillation (DWO) in parallel rectangular channels on inclined conditions. Test parameters were 3 MPa to 8 MPa for pressure, 300-800 kg/(m²•s) for mass velocity, 180-270 ℃ for inlet temperature and 0°-30° for angle of inclination. The effects of pressure, mass velocity, subcooling and angle of inclination on flow instability boundary parameters were investigated. Dimensionless subcooling number N_sub and phase change number N_pch were adapted to obtain flow instability boundary. An empirical correlation including Froud number and Δρ/Δρ_g was produced based on experiment results. The study shows that the inclined condition has little effect on DWO in the range of test parameters.