limited availability of low-salinity water in the northeastern semi-arid region of Brazil is one of the main constraints to the expansion of irrigated agriculture. In this context, the objective of this study was to evaluate the effects of irrigation with saline water on the salinity tolerance of guava during the rootstock formation phase. The experimental design was a randomized complete block in a 2 x 5 factorial scheme, consisting of two guava genotypes (Crioula and cv. Paluma) and five levels of irrigation water electrical conductivity (ECw: 0.3, 1.2, 2.1, 3.0, and 3.9 dS m-1), with six replicates. Stem diameter, plant height, fresh biomass of leaves, stems, and roots, and the accumulation of dry biomass in leaves, stems, roots, and total biomass were measured, along with Dickson quality index, transpiration rate, stomatal conductance, CO2 assimilation rate, and the absolute and relative growth rates in plant height. Irrigation using water with electrical conductivity above 0.3 dS m-1 inhibited stem diameter growth, root dry biomass, leaf transpiration, relative growth rate in height, and Dickson quality index in guava seedlings. Among the genotypes, Crioula showed greater growth, photosynthetic activity, and Dickson quality index under saline water irrigation, indicating its potential for use as a rootstock under semi-arid conditions.