The relativistic Doppler broadening of the line emission from both thermal and power-law particle distributions isinvestigated.We derive the exact analytic formulae describing the profiles.We find that the peak of the thermal line profilemoves to a higher frequency than the frequency in the rest frame of emitter for the high temperature case. For a power-law2p particle distribution (N(g)g), the line profile for the particle distribution of p52 is more like a continuum than a line,and the peak of it occurs at a higher frequency than the rest one. In the case of the high power-law index (p.2), the lineprofile peaks at the intrinsic frequency of the line and extends over a large frequency range in the blue wing, but sharplydrops in the red wing. The analytic formulae describing the line profiles presented in this work will be potentially useful infurther profile calculations on nuclear lines from different astrophysical systems.