Abstract: According to multiscale and multidirection contourlet transform and considering real image frequency spectrum characteristics, effects of contourlet lowpass filter on contourlet-based image fusion algorithms and ringing artifacts in fused images were analysed, and relations between lowpass filter and decomposing levels were discussed. Theories and experiments proved that better fusion results can be obtained with a narrow bandwidth lowpass filter, and that ringing artifacts can be eliminated by using a lowpass filter with positive coefficients. Fusion results using different lowpass filters and fusion rules were compared. Experimental results showed that choosing an appropriate lowpass filter can get a satisfying fusion result, with an easier fusion rule and less decomposing levels, which can reduce the fusion algorithm's complexity.