  In this article, we introduce and study Riesz bases in a separable
quaternionic Hilbert spaces. Some results on Riesz bases in a separable
quaternionic Hilbert spaces are proved. It is also proved that a Riesz basis in
a separable quaternionic Hilbert space a frame for the quaternionic Hilbert
space. Riesz sequences are defined and equivalence of a Riesz basis and a
complete Riesz sequence in a separable quaternionic Hilbert space is proved.
