Two borate chlorides LaB4O6(OH)(2)Cl and Ce-B4O6(OH)(2)Cl have been synthesized and characterized. Both of them exhibit structure similar to that of notable KBe2BO3F2 and feature two-dimensional [B4O6(OH)(2)](infinity) layers constructed by [B4O8(OH)](2) fundamental building blocks. Thermal analyses, infrared spectroscopy, UV-vis-NIR spectra, and second harmonic generation measurement were performed to investigate their physical properties. The results show that both of them have high decomposition temperatures and large second-harmonic generation responses (2.3 and 2.1 x KH2PO4, respectively), and LaB4O6(OH)(2)Cl possesses a deep-UV cutoff edge below 180 nm and large band gap. Moreover, the first-principle calculations were carried out to clarify the role of the electronic structure in determining the associated optical properties of LaB4O6(OH)(2)Cl. These results demonstrate that LaB4O6(OH)(2)Cl can be considered as a candidate for ultraviolet nonlinear optical material.