The compositional and structural properties of alkali metal ion exchanged Y-zeolites have been investigated by la number of analytical techniques and their catalytic activities were tested for NOx reduction in combination with a non-thermal plasma. The NOx conversion data for LiY, NaY, KY and CsY were measured by chemiluminiscent NOx meter in the temperature range of 100 to $350^{circ}C$. The initial activities of the catalyst at $150^{circ}C$ increased in the order LiY < KY < NaY < CsY in alkali series. The activity of CsY and NaY were increased and showed maximum at $200^{circ}C$ and then decreased in the plasma reactor, as the temperature increased. The activity of KY maintained same by $200^{circ}C$ and then decreased, whereas the activity of LiY decreased with the increasing temperature. The CsY catalyst, which showed the highest activity in alkali metal series, exhibits a NOx conversion efficiency of $80\%$ between $170{~}220^{circ}C$.