Several compositions of the type Sr x Yb 1 - x F 3 - x (x = 0.20, 0.25, 0.30. 0.33) were prepared by heating the well ground mixtures of appropriate amounts of SrF 2 and YbF 3 at 1100 o C. The substitution of Yb 3 + in YbF 3 by Sr 2 + for x = 0.25 and 0.3 leads to new single phasic fluorides with tysonite type structure. Quenching was shown to be essential to stabilize these phases. The XRD pattern of Sr 0 . 2 5 Yb 0 . 7 5 F 2 . 7 5 , i.e., SrYb 3 F 1 1 was fitted on a hexagonal unit cell with space group P6 3 /mmc with a = 3.9606(4) and c = 6.9731(5) Å. According to Rietveld refinements the as prepared SrYb 3 F 1 1 crystallizes in the disordered HT-form of the tysonite type structure. The magnetic measurements of Sr 0 . 2 5 Yb 0 . 7 5 F 2 . 7 5 show paramagnetic behaviour with a magnetic moment of 4.6 μ B which corresponds to the f 1 3 configuration of Yb 3 + .