Andorra doesn’t allow dual citizenship. Look at Chapter II under Article 7 – You will be renouncing your citizenship if you choose to be naturalized.
Naturalization- Renouncing existing foreign citizenships and residence in Andorra permanently for at least 20 years are required for naturalization. Look below for more information and contact details for naturalization on the Andorra Government Website: Afer Exteriors
Monetary Shortcut- If you invest EUR 400,000 you can get citizenship. No More Tax
Exceptions: If you are born in Andorra and move somewhere else- you can retain you nationality as long as the other country allows dual citizenship. For example is you are born in Andorra and move to the U.S. to apply for U.S. Citizenship you can keep your Andorran Nationality because the U.S. will not make you renounce your Andorran citizenship