Striker Natalia Padilla scored a late winner for Poland in the 84th minute from close range, converting a pass from winger Nadia Krezyman, Polish state news agency PAP reported.
The away win in Bucharest on Tuesday marked the second straight Nations League victory for Poland after their 2-0 defeat of Northern Ireland in the Baltic city of Gdańsk last Friday.
The Poles, the top seeds in League B Group 1, are ranked 28th worldwide by football's governing body FIFA, while Romania are No. 48 in the FIFA table.
Manager Nina Patalon's squad will take on Bosnia and Herzegovina in Gdańsk on April 4 in their next Nations League fixture.
Later this year, Poland will join 15 other teams from across Europe for the Euro 2025 tournament in Switzerland.
Poland have been drawn to play Germany, Sweden and Denmark in the group stage of this year's European football championships.
Poland head coach Nina Patalon. Photo: PAP/Adam Warżawa
The Polish team opens its Euro 2025 campaign against Germany on July 4.
Poland captain Ewa Pajor. Photo: PAP/Adam Warżawa
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Source: IAR, PAP, pzpn.pl