  We report the effect of doping Mn in the isostructural MgCNi$_{3-x}$Mn$_{x}$
(x = 0-0.05) compounds. Magnetic susceptibility, resistivity,
magneto-resistance, and specific heat studies show evidence of localized
moments and Kondo effect in samples with x$\neq$0. The rapid suppression of
superconductivity ($\sim$ -21K/at.% Mn) in these compounds is a consequence of
pair breaking effects due to moment formation on Mn.
