Purpose: The purpose of this study was to evaluate the difference between respiratory function and speech production, according to the seat surface inclination while in the sitting position. Methods: Respiratory function (FVC, FEV1) and speech production (inspiratory frequency, unit reading time, paragraph reading time) were measured in 3 sitting conditions: horizontal seat surface, seat surface tilted forward 15 degrees, and seat surface tilted backward 15 degrees. Results: We found that the mean values of FVC and FEV1 were statistically significant different according to three types of sitting positions (p<0.05). The following result was observed: forward tilted sitting > horizontal sitting > backward tilted sitting. There was no significant difference in speech production between the different positions. Respiratory function and speech production had a significantly negative correlation in the forward tilted condition and the backward tilted condition. Conclusion: This finding suggests that the seat surface inclination have an effect on respiratory function. Especially, forward tilted sitting may be an effective posture that may help increases the respiratory function.