Dianthus caryophyllus is an important ornamental plant globally. Tissue culture techniques have been used for the commercial production of carnation. However, micropropagation of carnation has been limited by the occurrence of hyperhydricity during shoot multiplication in vitro. The present study utilized rare earth elements (REEs) for reducing the incidence of hyperhydricity in micropropagated carnation during the multiplication stage. Nodal explants of D. caryophyllus ‘1130’ cultured in vitro for four weeks were cultured on the Murashige and Skoog medium containing 1.0 mg l^-1 6-benzyladenine and 0.5 mg l^-1 indole-3-acetic acid. The medium was supplemented with 0.05 or 0.1 mM of the REE in a form of lanthanum nitrate [La(NO₃)₃], cerium nitrate [Ce(NO₃)₃], or neodymium chloride (NdCl₃). Hyperhydricity occurred in approximately 71.1% of the plantlets cultured using the medium devoid of REE. Among the REE treatments, the least incidence of hyperhydricity (48.3%) was observed in the medium supplemented with 0.05 mM Ce(NO₃)₃. Although no significant difference was found in accumulation of superoxide or hydrogen peroxide among treatments, reduction of hyperhydricity was correlated with lower activities of antioxidant enzymes, such as catalase, guaiacol peroxidase, and ascorbate peroxidase. Moreover, the total soluble protein content was increased in the 0.05 mM Ce(NO₃)₃ treatment. Therefore, less incidence of hyperhydricity by 0.05 mM Ce(NO₃)₃ seems to be caused by decreased oxidative stress during axillary shoot multiplication. These results suggest that 0.05 mM Ce(NO₃)₃ supplement could be an option for reducing incidence of hyperhydricity in micropropagated carnations in vitro.