Nonhygroscopic single crystals of beta -Zn3BPO7 have been grown from the stoichiometric melt and characterized as a nonlinear optical crystal. The phase transition of beta -Zn3BPO7 into alpha -Zn3BPO7 is effectively suppressed by the appropriate heat treatment. This crystal is transparent down to 250 nm, and its nonlinear coefficient d(11) = 0.69 pm/V.