After representing Romania at the U-16 and U-18 levels, Niculae was promoted to the U-21 level. Niculae's form for Dinamo saw him selected for the Romania U-21 team to play Bulgaria U-21 on 3 March 1999, and he marked his debut with the second goal as Romania won 3–1. He played his first official match for Romania U-21 on 26 March, in a 0–1 defeat against Slovakia U-21, coming in as a substitute for Marius Luca in the second half. Despite he played all six remained qualifiers, Niculae hasn't scored a single goal as Romania failed to qualify at the European Championship. Since he was still eligible to play for Romania U-18, Niculae was called up by coach Gheorghe Cristoloveanu for 2000 European Under-18 Championship qualifiers. He scored a brace on the first match against Bosnia and Herzegovina in a 3–1 win, but he was sent off in the second match against Bulgaria alongside teammates Adrian Olah and Tiberiu Bălan, ending his career for Romania U-18. Romania drew in the final match against Ukraine, thus failing to qualify for the play-off.