Abstract: An investigation was conducted to isolate and characterize pathogenic bacteria in the gut of swimming crab (Callinectes) obtained from Lagos lagoon (28±2oC) and market frozen samples (0oC). The log10 of cfu/ml total value of 7.2 and 4.83 cfu/ml was obtained from fresh lagoon and market samples respectively. Pathogens isolated were Bacillus cereus, Escherichia coli, Proteus vulgaris, Salmonella sp, Streptococcus agalactiae, Vibrio sp, Staphylococcus aeureus and Micrococcus sp. Escherichia coli and Bacillus subtilis were more preponderant than other pathogens with log10 cfu/ml values of 5.90 and 3.0 (for Lagoon and market samples) and 5.81 and 4.47 (for lagoon and market samples) respectively. However, the log10 of cfu/ml for market samples for Bacillus subtilis was higher than Escherichia coli. On blood agar supplemented with sheep red blood cells, most isolates except few were ß- and α-haemolytic, demonstrating that they could be pathogenic strains. The degree of haemolysis were Bacillus cereus 34 (76%), Escherichia coli 46 (78%), Salmonella sp 33 (76.7%), Vibrio parahaemolyticus 40 (93%), Staphylococcus aureus and Bacillus subtilis were more haemolytic than Micrococcus sp, Streptococcus agalactiae and Proteus vulgaris. The occurrence of these pathogens in the swimming crab is of epidemiological and health significance.