Plants encounter many stress factors which affect their growth and development throughout their lifecycles because of their sessile nature. These stress conditions which can be originated by biotic and abiotic factors can adversely affect the quantity and quality of the product with leading to physiological and biochemical damage to crops. Plants have molecular response mechanisms for protecting and reducing negative effects of stress factors and these mechanisms can be divided in three groups, including homeostasis of ions and macromolecules, synthesis of protective molecules and formation and detoxification of reactive oxygen species (ROS). Homeostasis of macromolecules and ions is one of the response mechanisms of plants against dehydration and contains activation and inactivation of aquaporins and ion transport systems which play a role for controlling of water transmission and ion balance. The other stress response of plants is based on synthesis protective molecules such as low molecular weighted soluble substances or osmolites, heat shock (HSP) and LEA (late embroyogenesis abundont proteins) proteins. These molecules are participate in cell as an osmotic regulator and osmoprotectan. The last molecular responses of plants is the generation of enzymatic and non-enzymatic antioxidants which are responsible for synthesis and detoxificaiton of ROS under stress condition. Today, in biotechnology which has become one of the most popular research area, improving the adaptation and resistance of plants against stress conditions is primarily depends on a clear understanding of the effects of stress in plants. In this respect, increasing the sources and studies of stress molecular biology would be useful.