The properties of bismuth triselenide (BiaSea) are already known to a certain extent through the work of several authors, while it was still an open question whether there exists an individual solid phase of BiSe. Further information on this subject could be obtained by the successful growth and investigation of single crystals of both Bi~Se a and Bias % . X-ray analysis by means of goniometry, WeiBenberg, Laue, and Debye-Scherrer diagrams confirmed the known crystal structure of BizS% (ditrigonal scalenohedral; D~d-R-3m; with the hexagonal axes: a = 4"t5 ~k and ~=28"55 ]k, and 3 molecules per unit cell). As to BizSe 2 it cart be shown that it belongs to the same class but to a different space group (D~ d --P 3 I m or D~ d --P 3 m t ; hexagonal axes : a = 4' 15 A, c = 22.84 ~k, unit cell: 3 molecules, if the formula Bi2S % is adopted). Common to both is a subcell with the dimensions: a'= a = 4"15 A and c'= 5'71 A. The temperature dependence of electrical conductivity and Hail coefficient was measured on several specimens having different crystal orientations. The most striking difference is the high anisotropy of Biz Se a (~ra/(r c = t 0) as compared with Bi 2 Se a (aa/(r c < 2). All specimens turn.ed out to be n4ype. The room temperature carrier concentration observed was: n (Bias @ = 8.10 is cm -~ and n (Bi~Sea)= 4.t02~ cm -a, the carrier mobility: /~ (Bi2Sea) = 2-t0 a cm2/V . s and /z (BiaS%) = 20 cm2/V -s.