Chlorophyll fluorescence has been known as one of the indicators of photosynthetic status to various environmental stresses. The aims of this study were to assess the effects of environmental factors on lettuce chlorophyll fluorescent responses (Fv/Fm) and to develop an environment optimization model for lettuce growth using a simple genetic algorithm. High values of Fv/Fm were observed when environmental factors were 22-26°C ambient temperature, 15-23°C root zone temperature, 900-1,600 ppm CO₂ concentration, 0.4-1.3 m·s^-1 air current speed, and 65-85% relative humidity. As photosynthesis photon flux (PPF) increased over 150 μmol·m^-2·s^-1, Fv/Fm values were decreased. Principle compo-nent analysis was used to estimate the combined effects of six environmental factors on lettuce growth. The developed model fitted observed Fv/Fm values with an average standard error of 1.2%. An optimal environment for lettuce growth was estimated by the model to be 22°C ambient temperature, 20°C root zone temperature, 1,578 ppm CO₂ concentration, 1.3 m·s^-1 air current speed, 216 μmol·m^-2·s^-1 PPF, and 75% relative humidity. The Fv/Fm value can be a good indicator of plant stress level and thus a useful parameter to optimize the environment for plant growth.