The pseudo-binary Y(y)d(1-y)Ba(2)Cu(3)O(x)-Ba3Cu10O13 (y= 0, 0.2, 0.5, 0.8 and 1) phase diagrams have been constructed using in situ high-temperature optical microscopic observations. The range of the liquidus line and the peritectic decomposition temperature increased as the ratio of Nd to Y increased. The YyNd1-xBa2Cu3Ox single crystals were grown by the horizontal temperature gradient method. The chemical composition of the grown crystals, determined using energy dispersive X-ray analysis, showed that the Y/Nd ratio in the crystals increased with the increase in Y/Nd ratio in the solute used for crystal growth.