To estimate the portal of entry of Vibrio penaeicida in kuruma prawn (Penaeus japonicus), immersion and oral infection experiments were conducted with pre-treated and intact prawns. In immersion challenge, V. penaeicida produced 30% mortality in the shell-removed group at both 10⁸ and 10⁷ CFU/ml doses while in the eye-cut group, mortalities were 44% and 13% at 10⁸ and 10⁷ CFU/ml, respectively. In the intact group, 10% mortality was observed at 10⁸ CFU/ml and no mortality at 10⁷ CFU/ml after two weeks. The pathogen produced high mortalities in the orally incubated group, the median lethal dose (LD₅₀) being 10³-10⁴ CFU/animal. In the groups given V. penaeicida-inoculated kuruma prawn meat and V. penaeicida-contaminated commercial pellets, mortalities within 60 days were 10% and 20%, respectively. These results suggest that the main portal of entry of V. penaeicida is the gastro-intestinal tract although the cuticle (epidermis) or wounds can also be portals.