The objective of this study was to investigate the growth characteristics of sowthistle (Ixeris dentata Nakai) under different levels of light intensity (photosynthetic photon flux, PPF), electrical conductivity (EC) of nutrient solution, and planting density for efficient production in a closed-type plant factory system. Growth and yield of the plants were analyzed at EC 1.5 and 2.0 $dS{cdot}m^{-1}$ with PPF 100 and 200 ${mu}mol{cdot}m^{-2}{cdot}s^{-1}$. Further, growth and yield were measured under four different planting densities: a 15-cm between-row distance with within-row distances of 10, 15, 20, and 25 cm. Shoot dry weight and leaf photosynthetic rate all increased with increasing EC and light intensity. Shoot fresh and dry weights, chlorophyll content, and leaf photosynthetic rate were maximal at EC 2.0 $dS{cdot}m^{-1}$ with PPF 200 ${mu}mol{cdot}m^{-2}{cdot}s^{-1}$. For all planting densities, number of leaves and leaf width were not significantly different. Shoot fresh and dry weights per plant were not significantly different, however, shoot fresh and dry weights per area decreased with increasing plating densities. A linear relationship was observed between the number of leaves and days after transplantation. Based on the results, we suggest a nutrient solution of EC 2.0 $dS{cdot}m^{-1}$, PPF 200 ${mu}mol{cdot}m^{-2}{cdot}s^{-1}$, and planting density of $15{ imes}10$ cm for maximal growth and yield of sowthistle in a closed-type plant factory.