The present invention is a process for bio synthesis of nano arsenic trioxide defined by its low toxicity, higher bio availability and nano particle size with the aid of buttermilk, goat urine, dolichos biflorous and other plant materials such as ginger, momordica charantia and musa paradisiaca. The invention is carried out in different steps involving purification of crude form of arsenic trioxide by boiling it with buttermilk, goat urine and extract of dolichos biflorous in subsequent steps, followed by the trituration of the bio purified arsenic trioxide with extracts of ginger and momordica charantia in subsequent steps and heating of the dry product obtained after trituration with musa paradisiaca resulting in the production of novel nano arsenic trioxide. The product is effective in the treatment of various diseases including different types of cancer in animals and humans. The product obtained through the process is less toxic with higher bio availability.
