Nauru President Baron Waqa says China is trying to win over and dominate Pacific Island countries.
His comments came at the end of a five-day visit to Taiwan, where he met with President Tsai Ing-Wen.
Taiwan state media report that on Friday, President Baron Waqa reiterated support for Taipei, and rejected the One China policy.
Nauru is one of a dwindling number of countries recognising Taiwan, which Beijing claims sovereignty over.
Mr Waqa said China's policies were "designed to entice and hook up" countries in the Pacific.
He said Nauru and Taiwan would continue to work together in areas like fishing and medical aid.
At the end of a press conference on Friday, Mr Waqa played a song on a ukelele gifted to him by President Tsai Ing-Wen.