Hey Manpreet

It depens on which country you want to do pharmaceutical toxicology in.

In India you will have to :

Firstly take up science in your 11th and 12th class after which you can do a bachelors (or graduation ) in any of the science streams like Bsc in Environmental Science, Biochemistry, Botany or Zoology or the best thing would be to do  B.Sc. in Toxicology. After that you can go for  M.Sc. in Toxicology or Environmental Toxicology  and even go for a PhD.

There are various good institutes like Central Drug Research Institute, Lucknow (Uttar Pradesh)  and Indian Institute of Toxicology Research, Lucknow (Uttar Pradesh) amongst many others which a re ideal institutes for this course.