Resumo. The algaroba (Prosopis juliflora (Sw) D.C.) is an exotic species whose leaves have great potential for use in human and animal feeding, being highly nutritious, besides being considered efficient in the recovery of degraded areas and impoverished soils. Despite the growing demand for seeds and seedlings of this species, little is known about the physiological quality of their seeds. Therefore, the objective of this work was to characterize the fruit and seed biometry of the species, as well as to determine the temperatures and substrates for the germination and early development of seedlings. The number of seeds per kilogram and the water content of the seeds were determined. The length, diameter, weight, and number of seeds in each fruit and the thickness, width, length and weight of the seeds were analyzed. In the germination test, three temperatures (20, 30 and 20-30°C) were used under the regime of 14 hours of white light and two substrates (on paper and paper roll). Seed embedding curves, germination, germination speed index, shoot length, root length and seedling dry mass were determined. The biometric data indicate wide variability for the characteristics evaluated for fruits, however, the seeds present less variability. Temperatures of 30 and 20-30 °C and both substrates tested are efficient for conducting the germination test of algaroba seeds in the laboratory.