This work aims to determine the crop coefficie nt of the yellow passion fruit and to find irrigation levels that can raise the yield a nd quality of passion fruit production under the environmental conditions of the semiarid re gion of Piaui (Br). The experiment was conducted at the Projeto Piloto de Fruticultura Irrigada (Irrigated Fruit Culture Pilot Project) of the CODEVASF, in Santa Rosa, PI (06 ° 47 '5 6''S, 42 ° 17' 17''W). We used randomized blocks with six treatments and four replications, with four plants to a plot. The treatments (irrigation levels) were defined as percentages of the reference evapotranspiration (ETo): T1 (25% ETo), T2 (50% ETo), T3 (75% ETo), T4 ( 1 00% ETo), T5 (125% ETo) and T6 (150% ETo). It was installed a battery with three tensiom eters per treatment at depths of 0.10 m, 0.30 m and 0.50 m, to monitor the soil water. Determining the crop coefficient (Kc), we used the soil water balance, and for obtaining that, two batteries were installed, with tensiometers placed at depths of 0.10 m, 0.30 m 0.50 m within a radius of 0.30 m and 0.60 m from the stems of the plants in T4. The Kc values were estimated in the 41-240 days a fter transplanting (DAT). The irrigation le vels of 408.25 mm (T1), 463.41 mm (T2) 535.11 mm (T3), 609.98 mm (T4), 704.71 mm (T5) and 826.02 mm (T6) were applied on performing the experiment. We evaluated the morphological and physiologic al growth variables of yellow passion fruit (plant height, stem diameter, number of internod es, leaf area, leaf number and leaf water potential) and production traits (yield, fruit numb er, fruit weight, fruit transverse diameter and fruit longitudinal diameter). Analysis of varia nce showed that the irrigation significantly influenced stem diameter (P