Ninety-three asthmatic children and their caregivers were studied on their techniques of inhaler administration. Factors associated with the correct use of the device were also evaluated. Only 55.9% of the studied children demonstrated the correct technique in using their inhalation devices. In children using MDI (n = 42), the most common incorrect performance was the step of breathing in slowly at the same time with actuation (n = 17, 40.5%). Among those who used MDI-spacer (n = 51), all medication was given by their caregivers. The most common error was the step of waiting for 30 seconds prior to the next MDI actuation (n = 13, 25.5%). Factors related to the correct performance included duration of use for more than 1 year (p = 0.02), instruction of inhalation technique by trained technicians (p = 0.04) and the education level of the caregivers (p = 0.01). Our study demonstrates that incorrect technique during inhalation is common among Thai children with asthma and emphasizes an essential role of health professionals in regular evaluation of their patients and caregivers to ensure their correct application.