A class of cationic clays, montmorillonite (MMT) is a bio-inspired layered material possessing high internal surface area and high adsorption ability. MMT has attracted much attention as an oral delivery carrier, because it provides mucoadhesive property, which is a fascinating feature to across the gastrointestinal barrier. Furthermore, cationic drugs or bioactive molecules can be intercalated into the interlayer spaces by electrostatic interaction due to its good swelling property and high cation exchange capacity (CEC). However, a few researches on the toxicity of MMT were reported, although many attempts have been made to develop MMT as a delivery carrier for small bioactive molecules. In this study, we evaluated the cytotoxicity of MMT by measuring cell proliferation in short- and long-terms, membrane integrity, and oxidative stress. Moreover, the acute oral toxicity and pharmacokinetic studies of MMT were also carried out to determine the lethal dose 50% ($LD_{50}$) values and to elucidate their possible accumulation in the target specific tissues or elimination from the body, respectively, after oral administration. The results demonstrated that MMT could cause some cytotoxic effects at high concentration after long-time exposure, while any remarkable toxicity was not found in mice receiving up to the highest dose tested, 1,000 mg/kg. MMT could be absorbed into the body within 2 h, but it did not significantly accumulate in any specific organ. These findings will provide critical information about the potential toxicity of MMT, finally contributing to its sustainable development as an oral delivery carrier with safe level.