Sr1-xLnxNb2O6, Ln = La (x less-than-or-equal-to 0.4), Nd (x less-than-or-equal-to 0.3) solid solutions with a CaTa2O6-type structure have been studied. No superconductivity was found in the prepared samples down to 5K. The CaTa2O6 type crystal structure of Sr0.6La0.4Nb2O6 was refined from X-ray powder diffraction data : R(i)=0.054, R(p)=0.117. The oxidation process of the lanthanum-containing compounds was studied. A drastical decrease of the lanthanum content, accompanied by the formation of the cation vacancies at the Sr/La site occurs during oxidation.