Santos' spell ends after less than nine months, having been appointed in January this year as a replacement for Czeslaw Michniewicz, who left after Poland exited the 2022 FIFA World Cup at the round of 16 stage to France.
Santos had been tasked with qualifying Poland to the 2024 European Championships in Germany and 2026 FIFA World Cup to be held in USA, Mexico and Canada, but they find themselves fourth in their five-team group following a 2-0 defeat to Albania on Sunday.
A Polish FA statement said: "The Polish Football Association informs that as of September 13, 2023, coach Fernando Santos ceases to be the coach of the Polish national team."
The head of the FA Cezary Kulesza said: "I would like to thank coach Santos for his work with the national team and I wish him good luck in his next challenges."
Santos was quoted as saying: "Even though we are ending our cooperation, I am grateful to have led the Polish national team and I wish all the best to Poland and its people, who welcomed me so well when I lived here."
The 68-year-old had previously been in charge of Portugal and famously led them to European championship glory in 2016 and the inaugural UEFA Nations League in 2019.
Santos was relieved of his duties after Portugal were knocked out of the Qatar 2022 World Cup by Morocco at the quarterfinal stage.
