Hydrogen peroxide (H2O2) is one of the metabolic end products present in exhaled breath and exhaled breath condensate. High levels of H2O2 found in breath condensate are an indicator of airway inflammation and could be used for monitoring the condition of patients with chronic obstructive pulmonary disease. However, sampling conditions such as breath temperature, condensing temperature, flow rate and collection time can affect the intrinsic properties of H2O2 - its solubility, volatility, and decomposition rate. Sudden decreases to H2O 2 concentration may be due to the sampling conditions instead of the patient's health status. The decomposition rate and Henry's law constant for saturated H2O2 vapor (RH > 95%) within 22-42°C, which correlates to room temperature and range of human breath temperatures, are needed for better understanding and standardization of breath collection. In this study, we determined the effects of initial H2O2 concentration, temperature, and sampling time on the decomposition rate by comparing electrochemical measurements of H2O2 in simulated breath samples. Results showed the decomposition rate of H2O2 increased as the breath temperature and sampling time increased and the solubility of H 2O2 increased with increasing flow rate and condensing temperature during sampling. Prediction models for H2O2 sensing in exhaled breath sample were developed that could be used in the standardization of exhaled breath condensate collection.