Chlorophyll a fluorescence has been used as a major technique to monitor the photochemical reactions of photosynthesis. Generally at room temperature chlorophyll a fluorescence will be generated from photosystem (PS) II. Therefore chlorophyll a fluorescence can be used as a probe to study the alterations in PS II photochemistry. In this investigation a study has been made by using PAM kinetic spectrofluoremeter to characterize the alterations induced by Cd (NO3)2 in thylakoid membranes isolated from wheat (Triticum aestivum) primary leaves. The treatment of Cd (250-750 μM) caused an increase in Fo and decrease in Fv depending on the concentration. The increase in Fo clearly indicates the alterations in light harvesting complex whereas decrease in Fv shows the inhibition in the PS II catalyzed electron transport. Thus increase in Fo of thylakoid membranes can be used a tool identify the above heavy metal toxicity.