Growth by the micro-pulling-down technique (mu-PD) of homogeneous and crack-free fiber single crystals with composition Ba2Na1-xYbxNb5O15 (0 < x < 0.08) is reported. The effect of Yb3+ addition to barium sodium niobate (BNN, x = 0), having the tungsten bronze-type structure, was examined by room temperature X-ray powder diffraction and differential thermal analysis coupled to thermogravimetry. In the region of the monophased field the structure is tetragonal from x = 0.02 to 0.16. Volume change is mainly by variation of the a-axis length. Addition of Yb3+ to BNN could be effective for the production of high optical quality, crack-free, bulk crystals by the Czochralski technique.