Ostracod species living in 13 ponds (25 sample points) in Bardenas Reales de Navarra Natural Park and World Biosphere Reserve are studied for the first time. Nineteen species were identified, nine of them being the most abundant. According to statistical analyses (cluster and Correspondence Analysis), the distribution of ostracod species in this semi-arid area is mainly controlled by water conductivity and pH. The hydroperiod, sediment type, dissolved oxygen, altitude and vegetation cover play a secondary role. Thus, in semi-permanent waters with conductivity between 4.5 and 5.4 mS/cm and pH from 7.95 to 8.73 the most abundant species is Sarscypridopsis aculeata (Costa). In ponds with water conductivity from 0.3 to 2 mS/cm, pH between 7.1 and 7.78 and dissolved oxygen from 0.1 to 7.95 mg/l, Cypridopsis vidua (Müller) s the most abundant species. When the vegetation cover increases in this type of ponds, Limnocythere inopinata (Baird) and Potamocypris villosa (Jurine) appear as more abundant. Finally, in ponds with conductivity between 0.34 and 2.8 mS/cm and sporadic input of running waters llyocypris bradyi Sars, is the most important species. When the internal water current increases in these ponds, Pseudocandona albicans (Brady) appears as most abundant. However, the accumulation of dead organic matter within the bottom sediment of these ponds favours the decrease of dissolved oxygen and the development of Eucypris virens (Jurine). With this work, we contribute to the knowledge of the ostracod biodiversity of this semi-arid environment and the ecological preferences of this group.