A Poisson pseudo-maximum likelihood with fixed-effects gravity model is employed to assess the trade creation and diversion effects of the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP) and three ASEAN+1 regional trade agreements (RTAs), four RTAs in total, on Taiwan’s frozen tuna exports to the top 20 export destinations for six different types of frozen tuna, spanning the period from 2002 to 2021. Our findings show that the conclusion of the CPTPP, China–ASEAN RTA, and South Korea–ASEAN RTA does not significantly undermine Taiwan’s competitive advantage in frozen tuna exports. However, the conclusion of the Japan–ASEAN RTA poses a threat to Taiwan’s competitiveness, as evidenced by the slight trade diversion effects observed, suggesting Taiwan’s export advantage in frozen tuna (030342–yellowfin tuna and 030344–bigeye tuna) has decreased.