In this study, we select a catalyst with the highest activity to reduce NO with CO as a reducing reactant from four series of perovskites La1-xSrxBO3 where B = Mn, Fe, Co, or Ni. The cause for different activities is also closely examined by characterizing the perovskites by XRD, XPS, NO-TPD, and CO-TPR. Activity test results indicate that the LaFeO3 catalyst has the highest activity. Also, substituting La with Sr increases the activity in the Mn, Co, and Ni series. In addition, an optimal substitution fraction exists for each series, whereas adding Sr does not promote the activity of the LaFeO3 catalyst. The atomic ratio of B/(La + Sr) obtained from the XPS analysis can be correlated to the substitution fraction of Sr (x) and, subsequently, with the catalytic activity. By increasing x, this ratio initially increases but later decreases when the SrBO3 phase appears. Among the catalysts in the same series, the one with a higher B/(La + Sr) ratio on the surface yields a higher activity. The NO-TPD experimental results indicate that the NO adsorption plays an influential role in this catalytic reduction reaction. Moreover, the temperature range of NO desorption is the same as that of the reaction and the amount of NO desorbed is roughly proportional to the catalyst activity. The CO-TPR reveals that the reducibility of the catalyst is another factor influencing the activity. A catalyst having a larger fraction of Sr is more easily reduced. However, such reduction becomes difficult when the SrBO3 phase appears.