Background: Inhaler technique errors can affect the disease outcome through reduced deposition of medication in the lungs with certain errors were more likely to deter the optimum drug from reaching the lung. The objective of this study was to evaluate the pressurized metered-dose inhaler (pMDI) critical technique errors among asthma and COPD patients, and to investigate the predictors of those errors. Methods: A cross-sectional, observational, and multi-centered study conducted in 3 major hospitals in the state of Penang, Malaysia. Asthma and COPD patients aged 18 years or older consented to the study were consecutively recruited if they were at least on 1 pMDI without mouthpiece spacer or facemask space. Direct observation of the patient's technique was recorded using a standard checklist and certain steps in the checklist were pre-determined as critical steps. The number of patients missed or incorrectly performed the steps including the critical steps were documented. Using logistic regression, the factors associated with the critical errors were determined, and the correlation was evaluated between age and pMDI knowledge score with critical inhalation steps score. Results: Of 209 patients observed, only less than half (40.7%) could perform all the critical pMDI steps correctly. Low education level was the only factor associated with critical inhaler errors. The increased knowledge of their inhaled medication was found to positively correlate with the correct critical inhalation steps. The critical errors also increase with the increased age of patients. Conclusion: The majority of the study population make inhalation error particularly in critical steps. Training and education intervention programs may help patients with lower education level, as well as those of advanced age and lack of knowledge of their inhaled medication because those populations are at a greater risk of committing critical errors in their use of pMDI.