In this study, pigmentation (Chlorophyll a, Chlorophyll b and carotenoid), bioaccumulation, and oxidative stress response upon boron particles exposure were investigated in Chodatodesmus mucronulatus, unicellular algae. The Effects of acute exposure was measured by growing algae in BG-11 media supplemented with varying concentrations of boron particles for 72 h. Nano boron has increased chlorophyll content for 48 h. However, as exposure time was prolonged, nano boron was toxic to the algae. Micro boron particles also indicated similar effects. Nano boron increased chlorophyll b at 48 hours. On the other hand, levels of chlorophyll b seem to decrease for the remaining part. Bioaccumulation of the boron particles did not notably change upon varying particle concentration. Nano boron particles toxicity is conclusively seen at 72 h of exposure. Additionally, nano boron particles are concluded to be more toxic than micro boron to the Chodatodesmus mucronulatus.