"Looking from the military perspective, of course, it would be best, and for the protection of Poland as well, to have those missiles deployed at a certain distance from the Polish border, in the territory of Ukraine," he told a news conference in Kaunas.
"In that case, they would provide the best possible protection both for Ukraine and for Poland."
The Polish president underlined, however, that it is "up to our NATO ally Germany" to decide on the deployment of the missile system.
"So our allies will have to make this decision, because the systems are at their disposal", Duda said, adding that his duty as Poland's president "is to make sure that the territory of Poland would be protected as best as it can be".
"So, this is something which is obvious to me: it is my duty as president of Poland to protect first and foremost the Polish citizens and the Polish territory," he said.
Germany recently offered Warsaw Eurofighter planes and Patriot air defense missile batteries, and Polish Defense Minister Mariusz Blaszczak initially said he would accept Berlin's offer with "satisfaction".
However, the Polish government has changed its mind about the missile defense system and is now asking Berlin to send it to Ukraine instead.
Kyiv, which it seeks to protect Ukraine's airspace from Russia's continuing missile strikes on its energy and civilian infrastructure, has welcomed Warsaw's proposal, but Berlin is unlikely to accept it, fearing that it would significantly increase NATO's involvement in the conflict.