ABSTRACTA pot experiment with spinach (Spinacia oleraceae L. Fam.: Chenopodiaceae) was conducted aiming to investigate the effect of the addition of sewage sludge (SS) on soil substrate, the growth of spinach, and the plant interactions of CaxCd and ZnxCd. There were six substrates obtained by mixing soil and sludge in different proportions by volume (20:1, 10:1, 6.7:1, 5.0:1, 4.0:1, 3.3:1) and a control (only soil). The highest biomass was achieved in treatments 20:1 and 10:1. There was not a linear increase due to toxicity when SS was added in higher proportions. Sludge improved soil fertility by increasing organic matter and total N. Furthermore, in all plant parts of spinach, the Ca and Zn contents were synergistically interrelated with the Cd content, facilitating Cd uptake. The use of sewage sludge as soil amendment is not applicable on agricultural land due to the accumulation of Cd in plant.