Spherical TiO2 nanoparticles (npTiO(2)) were prepared by controlled hydrolysis of tetraethoxy orthotitanate under a nitrogen atmosphere. ZnO nanoparticles (npZnO) were prepared using hydrothermal methods. The crystal structure, chemical, thermal and morphological properties of npZnO and npTiO(2) were characterised using Fourier Transform Infrared Spectrometer, enery-dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscope techniques. The short- and long-term experiments were started with neonates taken from the same culture and laboratory condition. In the acute experiments, npTiO(2), npZnO, and cocktail concentrations were applied. 96h-LC50 values were 1.8, 0.7, and 0.1mgL(-1), respectively (p<.05). For the chronic experiments, different npTiO(2) concentrations were performed. 21d-LC50 value was 1.0mgL(-1) (p<.05). Morphometry became progressively worse in concentrations of more than 1mgL(-1) npTiO(2). Neonate and young individuals were more sensitive to death because of their low tolerance. This result was affected by population progeny and growth rates (p<.05). While control and 0.5mgL(-1) npTiO(2) groups were determined as growing population, 1.5 and 2mgL(-1) npTiO(2) groups had decreased population size as R-0 values. Consequently, the relationships between nanoparticle accumulation within Daphnia magna and its population structure and body morphometry for each concentration were important indicators. Its tolerance level to nanoparticles under laboratory conditions reflected its replacement and behaviour in the ecosystem.