The rare-earth borate-nitrates Nd[B 5 O 8 (OH)(H 2 O) 0.85 ]-NO 3 ·2H 2 O and Sm[B 5 O 8 (OH)]NO 3 ·2H 2 O have been prepared by hydrothermal synthesis. Both structures crystallize monoclinically in the space group P2 1 /n (no. 14) with a = 642.85(2), b = 1552.58(4), c = 1070.52(2) pm, = 90.39(1)°, and V = 1068.44(5) nm 3 for the neodymium compound, and a = [a]