Canned tuna can be produced from different types of the Scombroid fish family. It is a product from fish meat that goes under heat processes after several preparation and production stages in order to be appropriate for commercial purposes. One of the main problems with this product is histamine poisoning. Products with high level of histamine cause different kinds of disease like urticaria, diarrhea, anaphylactic shock and, finally, death. In this study, International Organization for Standardization 22000:2005 requirements was implemented in a canned tuna-processing unit. Histamine content was measured by gas chromatography (GC) method throughout workstations which were mentioned above. Histamine levels were measured before and after all the workstations such as frozen fish reception, temporary storage in -18°C defrosting, deheading-descaling-draining viscera, precooking, cleaning and segmenting, and sterilization by GC method. We found out that frozen fish reception, deheading-descaling-draining viscera, and cleaning-segmenting reduced histamines, 27.46%, 27.88%, and 60.87%, respectably. Also, the maximum histamine content reduction was in the cleaning-segmenting workstation. The results in this study can be applied to decrease the histamine level in canned tuna products and protect people from the above-mentioned diseases