In this paper we investigate an exact spectrum of quasi normal modes (QNMs) for perturbations of a scalar field coupled non-minimally with the Einstein tensor of an uncharged, non-rotating Banados, Teitelboim, and Zanelli (BTZ) black hole in three-dimensional spacetime. Due to the geometry around the black hole, the scalar field encounters an effective potential barrier. We study this potential numerically and derive exact numerical results for the greybody factors (GFs) and discuss their profiles in terms of the coupling constant and black hole parameters. We then proceed to derive the Hawking radiation spectrum for BTZ black hole. 1 d.mahdavian@hsu.ac.ir arXiv:1810.08991v2 [hep-th] 29 Aug 2019Recently it has been devoted a lot of studies of gravitational theories to modification of Einstein's gravity.One class of these theories concern the scalar-tensor theories, such as Horndeski theory which gives a second order field equations in four dimensions [1][2][3]. The Lagrangian of this model contains a term for coupling of a scalar field with curvature tensors. This kind of coupling has interesting cosmological implications [4][5][6][7]. The coupling of the scalar field to Einstein tensor can be regarded effectively as a cosmological constant [6]. On the other hand, this scalar-tensor concept is also intriguing in threedimensional general relativity (GR). Vanishing Newtonian potential in three-dimensional GR disqualifies it to serve as a compatible theory for three-dimensional gravity while the proper description is obtained by dimensional reduction of four-dimensional GR to a scalar-tensor theory in three dimensions. The other standard approach which we will not discuss it here is the addition of higher derivative corrections to GR to produce massive gravity theories in three dimensions proposed in Refs. [8][9][10][11][12]. The nice feature of these theories is that there are different kinds of black hole solutions to their equations of motion [13]-[21], however the most reputed asymptotically AdS one is the BTZ black hole [22]. Within the framework of this theory, the existence of black holes is anticipated, which is an appropriate ground for understanding many aspects of gravity theory.The stability of a black hole can be examined by the study of dynamical behaviors of the perturbations in its background spacetime. The natural vibrational modes of these perturbations in the spacetime exterior to an event horizon are called quasi normal modes (QNMs). The corresponding frequency