Quantum dots (QDs) nanoparticles are increasingly being used for electronics devices, solar energy generation and medical imaging applications. While the new properties of nanoparticles are more and more studied, little is known about their interactions with aquatic organisms. As a primary producer, phytoplankton serves as an important component of the aquatic ecosystem. According to our bibliographic search, no reports were found on the evaluation of ecotoxicity of QDs in Pseudokirchneriella subcapitata. In this study, QDs were evaluated using ecotoxicological bioassays (cellular toxicity models and potential indicators of the impact in aquatic ecosystems) with the microalgae P. subcapitata. With ecotoxicity concentrations of 0, 1, 2, 3 and 4 nM of QDs with P. subcapitata at 96 h exposure a mean inhibitory concentration of growth (IC50) of the microalgae P. subcapitata IC50 = 1,94 nM of QDs(a) was obtained for orange fluorescence; IC50 = 1.68 nM of QDs(r) for red fluorescence, and IC50 = 2.03 nM of QDs(v) for green fluorescence, observing the following order of sensitivity: QDs (r) ˃ QDs (a) ˃ QDs (v). The toxicity of the QDs are evident by the type of fluorescence detected in the standard solution 4 M of QDs and 10-1M. The images of confocal microscopy of fluorescence showed adhesions of QDs in microalgal cells until low concentrations with high growth rates of P. subcapitata at concentrations of 1 nM compared to concentrations of 10-1 M of QDs nanoparticles with low growth rates.