This paper is concerned with the study of reflection of longitudinal displacement waves from the flat boundary of an elastic half-space containing a distribution of void pores. The half space is under the action of a uniform magnetic field and the magnetic field is applied in such a direction that the problem can be considered as a two dimensional one. The critical value of the frequency has been detected. Amplitude ratios have been presented. The effects of magnetic field on various subjects of interest are discussed and shown graphically. © 2013 Elsevier Ltd. All rights reserved.