This study was conducted on a variety of lettuce curly (Lactuca sativa var. Crispa) called Caipira. The purpose was to elucidate the effects of cadmium stress on the plant???s metabolic processes, response to cadmium stress and adaptation mechanisms developed against cadmium stress with the use of proline treatments. Hydroponic experiments were conducted in a climate chamber supplied with a controlled atmosphere (15??2??C 13 h dark, 22??2??C 11 h light and 70% relative humidity). When the seedlings formed new roots and had 4-5 leaves, initially 5 mM, 10 mM, 15 mM proline solutions were sprayed on the leaves of a group of seedlings 4 days before applying cadmium stress, then the plants were exposed to 40 ppm cadmium. The other group was sprayed with 5 mM, 10 mM, 15 mM proline solutions just before applying cadmium stress. Yet another group of plants was subjected only to cadmium stress without proline treatments. Therefore, 8 different treatments were tested: Control (0 ppm cadmium), only cadmium (40 ppm), proline (5 mM, 10 mM, 15 mM) 4 days before the stress + cadmium, proline (5 mM, 10 mM, 15 mM) + cadmium stress together. The present findings revealed that 5 mM proline dose was relatively effective in mitigation of negative effects of Cd stress on plant physiological and metabolic processes. Proline treatments at this dose were found to be effective in alleviating the negative effects of Cd stress on growth parameters of curly lettuce plants. It was also concluded that such effects of external proline treatments varied with the treatment dose and timing.