The selective encapsulation behavior of cucurbit [5]uril and its lanthanide-capped molecular capsule toward nitrate and chloride ions has been investigated. Using fluorescence spectroscopy, the metal-free host has been demonstrated to selectively include nitrate ion. In contrast, the lanthanide-capped molecular capsule showed preference toward the inclusion of chloride ion. Solid-state structures of the nitrate and chloride inclusion complexes with the La(III)-capped molecular capsule have been crystallographically determined.