Detailed near- and far-field acoustic measurements were conducted for two circularstepped nozzles with 30 deg and 60 deg design inclinations at over- and perfectlyexpandedsupersonic jet flow conditions and compared to those for a circular nonsteppednozzle. Far-field acoustic results show that stepped nozzles play an insignificant role inaltering noise emissions at perfectly expanded condition. At an over-expanded condition,however, the longer stepped nozzle produces significant noise reductions at the sidelineand upstream quadrants, while the shorter stepped nozzle does not. Noise spectra analysisand Schlieren visualizations show that noise reduction can be primarily attributed tomitigations in the broadband shock-associated noise (BSAN), due to the ability of the longerstepped nozzle in suppressing shock strengths at downstream region. Near-fieldacoustic measurements reveal that the source region, as well as the intensity of turbulentand shock noises, are highly sensitive to the stepped nozzle configuration. Furthermore,BSAN seems to be eliminated by the longer stepped nozzle in near-field region due to theshock structure modifications.