Purpose: This study was done to investigate the relationship of knowledge related to disease, awareness and practice of inhaler use in asthmatic patients. Method: The participants in this research were 124 patients with asthma who used inhalers, and were admitted to hospital or attended outpatient asthmatic clinics. Data were collected using a self-administered questionnaire which consisted of demographic characteristics, illness-related characteristics, and tools to measure knowledge of disease, awareness and practice related to inhaler use. Results: Knowledge related to disease was statistically significantly different for age (p<.001) and marital status (p=.017). The mean score for awareness of inhaler use was significantly higher than the mean score for practice in inhaler use (p<.001). There were significant correlations between awareness and practice of inhaler use (p<.001), knowledge related to disease and awareness of inhaler use (p<.001), and knowledge related to disease and practice of inhaler use (p<.001). Conclusion: Results indicate that due to the variation in degree of illness in patients with asthma, there is a need to develop appropriate education programs for people of different ages and also precise ${alpha}$ II content for use of inhalers method of checking capacity washing and storing as well as directions about different kinds of the inhalers.