Novel compounds CeNb7O12 and PrNb7O12 isostructural with LaNb7O12 have been synthesized. XPA data show that LnNb7O12 (Ln = La, Ce, Pr) refer to the sp. gr. P21/c, Z = 4 with lattice parameters a = 10.764(2), 10.743(2), 10.738(4) Å; b = 9.192(2), 9.146(2), 9.137(3) Å; c = 10.313(2), 10.304(2), 10.303(3) Å; = 104.25(2), 104.31(2), 104.21(3), respectively. The unit cell parameters of the LnNb7O12 phases decrease with the РЗ-ion radius r(La3+) > r(Ce3+) > r(Pr3+). In the Nd(Sm) –Nb – O systems, phases NdNb7O12 and SmNb7O12 do not form.