Use of a silicotitanate composition, wherein the composition comprises a silicotitanate having a sitinakite structure and niobium, and has at least two or more diffraction peaks at X-ray diffraction angles selected from the group consisting of 2θ = 8.8 ± 0.5°, 2θ = 10.0 ± 0.5°, and 2θ = 29.6 ± 0.5°, wherein the 2θ is a value of X-ray diffraction angle in a powder X-ray diffraction pattern measured using a general X-ray diffractometer and the measurement conditions are as follows: Radiation source: CuKα-ray, λ = 1.5405 Å Measurement mode: step scan Scan condition: 0.04°/second Divergence slit: 1.00 deg. Scattering slit: 1.00 deg. Receiving slit: 0.30 mm Measurement time: 3.00 seconds Measurement range: 2θ = 5.0° to 60.0°, in an adsorption method for at least any of cesium and strontium, wherein the composition has at least X-ray diffraction angles 2θ and X-ray diffraction peak intensity ratios that are shown in Table 1 below: [Table 1] X-RAY DIFFRACTION ANGLE 2θ [°] XRD PEAK INTENSITY RATIO 8.8 ± 0.5 5 OR MORE AND 20 OR LESS 10.0 ± 0.5 5 OR MORE AND 20 OR LESS 11.3 ± 0.5 100 29.6 ± 0.5 5 OR MORE AND 40 OR LESS, wherein the XRD peak intensity ratio in Table 1 is a relative value of XRD peak height at each 2θ relative to an XRD peak height when the peak intensity at 2θ = 11.3 ± 0.5 is taken as 100. wherein the composition comprises a silicotitanate having a sitinakite structure and niobium, and has at least two or more diffraction peaks at X-ray diffraction angles selected from the group consisting of 2θ = 8.8 ± 0.5°, 2θ = 10.0 ± 0.5°, and 2θ = 29.6 ± 0.5°, wherein the 2θ is a value of X-ray diffraction angle in a powder X-ray diffraction pattern measured using a general X-ray diffractometer and the measurement conditions are as follows: Radiation source: CuKα-ray, λ = 1.5405 Å Measurement mode: step scan Scan condition: 0.04°/second Divergence slit: 1.00 deg. Scattering slit: 1.00 deg. Receiving slit: 0.30 mm Measurement time: 3.00 seconds Measurement range: 2θ = 5.0° to 60.0°, in an adsorption method for at least any of cesium and strontium, wherein the composition has at least X-ray diffraction angles 2θ and X-ray diffraction peak intensity ratios that are shown in Table 1 below: [Table 1] X-RAY DIFFRACTION ANGLE 2θ [°] XRD PEAK INTENSITY RATIO 8.8 ± 0.5 5 OR MORE AND 20 OR LESS 10.0 ± 0.5 5 OR MORE AND 20 OR LESS 11.3 ± 0.5 100 29.6 ± 0.5 5 OR MORE AND 40 OR LESS Radiation source: CuKα-ray, λ = 1.5405 Å Measurement mode: step scan Scan condition: 0.04°/second Divergence slit: 1.00 deg. Scattering slit: 1.00 deg. Receiving slit: 0.30 mm Measurement time: 3.00 seconds Measurement range: 2θ = 5.0° to 60.0°, in an adsorption method for at least any of cesium and strontium, wherein the composition has at least X-ray diffraction angles 2θ and X-ray diffraction peak intensity ratios that are shown in Table 1 below: [Table 1] X-RAY DIFFRACTION ANGLE 2θ [°] XRD PEAK INTENSITY RATIO 8.8 ± 0.5 5 OR MORE AND 20 OR LESS 10.0 ± 0.5 5 OR MORE AND 20 OR LESS 11.3 ± 0.5 100 29.6 ± 0.5 5 OR MORE AND 40 OR LESS, wherein the XRD peak intensity ratio in Table 1 is a relative value of XRD peak height at each 2θ relative to an XRD peak height when the peak intensity at 2θ = 11.3 ± 0.5 is taken as 100.