Crystal Mountains (Monts de Cristal) is a group of low mountains (or hills, as all peaks are below ) inland of the Atlantic coast of Equatorial Guinea, Gabon, the Republic of the Congo, the Democratic Republic of the Congo, and Angola. It is the edge of the interior Woleu-Ntem Plateau against the coastal lowland which has a steep descent deeply cut by streams and waterfalls.
Part of the area is preserved in Gabon as the Crystal Mountains National Park. Mont Mbilan is the highest point (about ) in the park. Seni Mont () receives the highest rainfall in all of Gabon ( per year).
Two species of frogs, Leptopelis crystallinoron and Leptodactylodon stevarti, are only known from the Crystal Mountains.