Rainbow Rare Earths said chief executive Martin Eales had stood down with immediate effect.
Eales had been replaced by George Bennett, who had led companies including Shanta Gold, OreCorp and Karo Power and had more recently established MDM Engineering.
Eales had been CEO of Rainbow Rare Eaths since 2014.
'I would like to thank Martin for his support during the early stages of Rainbow's development, IPO, and initial production,' chairman Adonis Pouroulis said.
Bennett said he would focus on stabilising production at the company's Gakara project in Burundi and develop an understanding of the deposit.
At 9:57am: (LON:RBW) Rainbow Rare Earths Ltd share price was -0.55p at 2.7p