Single crystals of the new compounds LnZn(B5O10) (Ln = (A) Ce3+, (B) Nd3+, (C) T b3+) were obtained by using a B2O3 flux technique. X-ray investigations led to space group C2h5-P21/n (Nr. 14) with lattice parameters: (A) a = 874.5(1), b = 761.4(1), c = 950.0(1), β = 92.80(1)°, (B) a = 868.6(2), b = 760.9(2), c = 946.0(2), β = 92.99(2)°, (C) a = 858.2(2), b = 760.5(2), c = 939.3(2), β = 93.56(2)°, Z = 4. The structure is isotypic with CoSm(B5O10) and is characterized by two-dimensional infinite 2∞ (B5O 10)5- ions. Ln is tenfold coordinated by oxygen, and Zn2+ occupies distorted ZnO6 polyhedra.