In our study, we present responses of Antarctic strain of filamentous alga Zygnema sp. collected at James Ross Island (Antarctica) to application of variuos uncouplers of pri-mary photosynthetic processes. We exposed the alga to different concentrations of nigericin, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), dithiothreitol (DTT), methyl viologen (MV) and hydrogen peroxide (H2O2) in order to test stability of photosystem II, involvement of non-photochemical quenching, and PS II functioning under combination of moderate light with particular uncoupler. Oxidative stress tolerance was tested by the combination of hydrogen peroxide (H2O2) and moderate light. Time courses of FV/FM, FPSII, NPQ and qF0 were investigated and particular effects of the above-specified chem-icals discussed. Moderate doses of uncouplers allowing partial recovery, and the doses causing full inhibition of PS II were specified.