Lanthanide tantalite LnTaO4 (Ln= La, Nd, Sm, Dy, Er and Tm) was synthesized by a solid state reaction between mixed powders of Ln2O3 (Ln=La, Nd, Sm, Dy, Er and Tm) and Ta2O5. The single-phase LnTaO4 was prepared by sintering at temperatures of 1423-1673 K in air. The SEM observation showed that the particles were provided with the growth steps and the depeloped facets. The photocatalytic activity for water splitting of LnTaO4 prepared was measured under UV light irradiation. The activity obtained was higher than that previously reported. These results suggested the crystallinity of LnTaO4 photocatalysts correlates closely with the efficiency of water splitting.