The authors report on the purification and characterization of mannan‐binding proteins (MBP) isolated from porcine serum. The MBPs were purified by use of PEG precipitation, affinity chromatography on mannan‐Sepharose, protein A‐ and anti‐porcine IgM‐Sepharose followed by gel filtration. The MBP proteins were collagenase sensitive and showed γ1‐γ2‐electrophoretic mobility. The MBP designated pMBP‐28 had a molecular mass of 28 kDa when analysed on SDS‐PAGE under reducing conditions and eluted corresponding to a molecular mass of approximately 700 kDa on gel filtration chromatography. Electron micrographs of pMBP‐28 revealed an oligomeric protein similar to rodent MBP‐A and human MBP but with a predominance of penta‐ and hexameric molecules. Another protein designated pMBP‐27 was composed of peptides of 27 kDa and had an Mr of 300–350 kDa on gel filtration chromatography. Electron microscopy of pMBP‐27 showed dimer and trimer molecules; the trimers without distinct stalk regions. The N‐terminal 26 (pMBP‐27) and 24 (MBP‐28) amino acid residues showed 54% and 58% identity with human MBP. pMBP‐28 showed a higher degree of sequence similarity to rat and mouse MBP‐A (60% identity) than to mouse and rat MBP‐C (41–45% identity). Both pMBPs exhibited Ca2+‐dependent binding to D‐mannose immobilized on agarose but no significant binding to N‐acetyl‐D‐glucosamine‐ or fucose‐agarose. The results further suggested the presence of a third pMBP which copurified with pMBP‐27 but this protein was not sequenced.