High salt stress involves ionic stress as well as osmotic stress. In this work we have tried to differentiate between the ionic and osmotic effects of salt stress on the basis of their ability to cause changes in PS II heterogeneity. PS II heterogeneity is found to vary with environmental conditions. Osmotic stress caused no change in the Q(B) reducing side heterogeneity and a reversible change in antenna heterogeneity. The number of Q(B) non-reducing centers increased under ionic stress but were unaffected by osmotic stress. On the other hand ionic stress led to a partially irreversible change in Q(B) reducing side heterogeneity and a reversible change in antenna heterogeneity. In response to both ionic and osmotic effect, there is conversion of active PS IIα centres to inactive PSIIβ and γ centres.