Halophytic plants have developed different strategies to survive and complete their life cycles under high concentrations of salts especially NaCl. Important features of salinity tolerance involve the production of various osmolytes, such as proline, glycine betaine, sugars, and ion compartmentalization. We supposed that these unique features could be also used in response to heavy metal stress. To test this hypothesis, we studied the effects of cadmium (Cd) on two species of a congeneric pair: the halophyte Juncus gerardii and glycophyte (non-halophyte) Juncus inflexus cultivated in vitro and in vivo. Their different salinity tolerance was evidenced by cultivation on media containing 100 and 300 mM NaCl. Only J. gerardii was able to grow well on medium with 300 mM NaCl for 28 days. In addition, both species were cultivated on media supplemented with Cd. The concentrations of Cd and proline in plant roots and leaves were measured after 2, 5, and 7 days in in vitro culture and after 7, 14, and 28 days in hydroponic solution. The accumulation of Cd did not significantly differ between these two species regardless of cultivation conditions (in vitro or hydroponic solution). However, the halophytic plant J. gerardii transported higher amount (128%) of Cd to shoots than J. inflexus and the free proline content significantly increased in response to cadmium exposure. The addition of NaCl (100 mM) decreased by 2.32 fold the accumulation of Cd and by 2.22 folds the proline content in J. gerardii.