A family of lamellar mesostructured n-alkylamine borophosphates, denoted C(n)A-BPO (BPO stands for inorganic borophosphate layer; n = 9-15, the number of carbon atoms in the n-alkylamine chain) has been prepared hydrothermally at 160 degrees C by using neutral n-alkylamines as templates. Those C(n)A-BPO compounds were characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric measurentents, and differential thermal analysis (TG-DTA) as well as chemical analyses. Interestingly, these compounds may form a bilayer, a monolayer, or mixed state of bilayer and monolayer structures depending on the content of n-alkylamine. Linear relationships for both bilayer and monolayer compounds were observed between the interlayer distances and the numbers of carbon atoms in the n-alkylamine chain. The thickness of the inorganic layers, the arrangement of n-alkylamine in the interlayer space, and the composition of the compounds are proposed.