Synthetic analogues of the minerals natisite and for the first time of paranatisite were prepared hydrothermally at 200 °C in the system Na2O–TiO2–SiO2–H2O. The obtained powder x-ray diffraction (XRD) patterns were interpreted by the Powder Data Interpretation (PDI) software package. As a result improved indexing and unit cell parameters refinements of these two phases were achieved. Synthetic natisite is tetragonal, space group—P4/nmm, a=0.649 67(8) nm, c=0.508 45(11) nm, V=0.214 50(10) nm3, Z=2, Dcal=3.13 g.cm−1, F30=37.48, M20=52.79. Synthetic paranatisite is orthorhombic, space group—Pmma, a=0.983 86(29) nm, b=0.919 23(19) nm, c=0.481 84(12) nm, V=0.435 78(19) nm3, Z=1, Dcal=3.01 g.cm−1, F30=16.42, M20=29.21.