 After spending six months as a free agent, Niculae signed a six-month deal with German Bundesliga side Mainz 05 on 12 December 2006.On 13 January 2007, he scored his first goal for Mainz in a friendly match against Hannover 96.He made his official Mainz debut as a substitute in the 1–0 win against VfL Bochum on 27 January 2007.