evidence: All dogs travelling to the Republic of Ireland are required to have either an Animal Health Certificate (AHC) or an EU-issued pet passport with a valid rabies vaccination in. GB-issued pet passports are no longer valid for travelling to the EU, and have been replaced with AHCs. [...] Technically, because you are entering the EU when travelling from Northern Ireland to the Republic of Ireland, you need to follow the EU rules when taking a dog, which includes getting an Animal Health Certificate issued and tapeworm treatment administered (as outlined above in the travelling to the Republic of Ireland from Great Britain section). If you entered Ireland through Northern Ireland but are planning on returning to Great Britain from the Republic of Ireland then we would definitely recommend following the steps above for travelling to the Republic of Ireland. This is because they will likely be checking documents at the border between the Republic of Ireland and Great Britain so they will want to see a valid Animal Health Certificate or EU pet passport.