Auxins play an important role in cluster root (CR) development in some species under low P conditions. However, the mechanism for CR induction in Embothrium coccineum J.R. Forst. & G. Forst remains unknown. Therefore, the aim of this work was to determine the effect of auxin on CR induction in E. coccineum, under low P conditions. For this, plants of E. coccineum were grown under P sufficiency and deficiency, and were treated with exogenous auxin and an auxin transport inhibitor. Phosphorous concentration in leaves, proportion of the total root allocated to CR mass (CRA), CR number (CRN), CR mass (CRm), and individual CR mass (ICRm), were measured. The number of CR showed a negative correlation with P concentrations in leaves. Furthermore, application of auxin in plants grown under P deficiency increased the CRA in a 50% and CRN in a 60%. The values of all parameters measured in plants grown under P deficiency conditions were reduced to less than half that observed in control plants, after foliar application of auxin transport inhibitor. However, no difference was observed when auxin was applied in plants grown with P supply. These results suggest that P and auxin are important factors for CR induction in E. coccineum.