A honeycomb structural body comprises one or plural pillar-shaped porous ceramic members in which many through-holes are arranged side by side in a longitudinal direction through partition walls and either one end portions of these through-holes are sealed.The partition wall forming the structural body has a surface roughness of not less than 10 .mu.m as a maximum roughness Rz defined in JIS B0601-2001 and an average pore size of 5-100 .mu.m in a pore distribution measured by a mercury pressure method, and satisfies the following relationship: A.gtoreq.90-B/20 or A.ltoreq.100-B/20 when a ratio pores having a pore size of 0.9-1.1 times the average pore size to total pore volume is A (%) and a thickness of the partition wall is B (.mu.m), and there is proposed an effective honeycomb structural body having excellent pressure loss and catching efficiency and a high catalyst reactivity.