ABSTRACT The intercropping system is characterized by interspecific competition and leads to one of the most limiting abiotic factors for high plant yield in this cropping system. Plants under low light can carry significant weight in physiological parameters that can limit growth. Light is one of the abiotic factors that limits productivity; in the present study, it was hypothesized that tomato (Solanum lycopersicum L.) and lettuce (Lactuca sativa L.) intercropping in different transplanting periods promotes changes in gas exchange, photosynthetic pigments, and biomass accumulation in two lettuce cultivars. An experimental study was carried out in Jaboticabal, Sao Paulo, Brazil. The treatments consisted of a combination of the following factors: lettuce (one ‘Lucy Brown’ plant between two tomato plants and two ‘Vanda’ plants between tomato plants), two cultivation systems (intercropping and monoculture), and four lettuce transplanting periods (0, 7, 14. and 21 d after tomato transplanting). The experiment was a randomized block with a 3 × 2 × 4 factorial design and four replicates. Transpiration and stomatal conductance were reduced in lettuce by insterspersing plants under a monoculture system. Lettuce-tomato intercropping severely reduced photosynthesis, fluorescence, chlorophyll pigment content, and DM accumulation. Therefore, ‘Vanda’ is better than ‘Lucy Brown’ for intercropping with tomato.