The purposes of acute toxicity testing are to obtain information on the biologic activity of a chemical and gain insight into its mechanism of action. The information on acute systemic toxicity generated by the test is used in hazard identification and risk management in the context of production, handling, and use of chemicals. For a classical LD50 study, laboratory mice and rats are the species typically selected. This book gives a short review of methods for acute toxicity testing with the emphasis on the Up and Down Method as per OECD Guidelines 425. Furthermore, this book consist of one research work on acute oral toxicity studies performed by authors.