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Antibacterial proteins are an important part of the innate immune system for all animals. The aim of the present work was to identify and characterise antibacterial proteins/peptides in serum of Clarias gariepinus. Antibacterial proteins/peptides were isolated from the serum of Clarias gariepinus using ammonium sulfate precipitation and further isolation on Sephadex G-50 column chromatography. Two fractions, namely, AP 1 and AP 2 associated with two absorption peaks at 280 nm were obtained. The antibacterial activity of AP 1 and AP 2 was tested against Escherichia coli, Aeromonas hydrophila and Edwardsiella tarda. AP 1 exhibited strong inhibitory activity against E. coli, A. hydrophila and E. tarda, and inhibited E. tarda best. AP 2 had also higher inhibitory activity against E. tarda than againstA. hydrophila, but it had not inhibitory activity againstE. coli. Protein profiles of AP 1 and AP 2 were determined by Laemmli SDS-PAGE system. The result showed that the AP 1 had a broad range of proteins/peptides with molecular weights ranging from about 9.5 kDa to over 66 kDa, and a 27 kDa protein/peptide was the most abundant than others, while the AP 2 had only 1 distinct protein band, which molecular weight was about 3.8 kDa.