1, 3-Butadiene is a cigarette smoke constituent with great contributions to smoke cancer risk. 1, 3- Butadiene is also an important chemical used in the production of synthetic rubber. 1,3-Butadiene has been categorized as a human carcinogen by the International Agency of Research on Cancer. Crotonaldehyde is an ubiquitous chemical that exists in the environment and endogenously, and is one of the most important aldehydes of human health concern. Crotonaldehyde has been shown to cause adverse biological effects in cell culture and animal studies, such as oxidative stress, inflammation, reacting with DNA and protein, mutation induction, and carcinogenicity. Studies have demonstrated that Crotonaldehyde is involved in human diseases, such as chronic obstructive pulmonary disease (COPD), Alzheimer''s disease, etc. This book reviewed the physical, chemical, and biological characteristics of 1, 3-butadiene and crotonaldehdye and evaluated their toxicological effects in cell cultures and in experimental animals.