Objectives The purpose of this study was to investigate the correlation between gastric emptying measured by ultrasonography and Korean medical instruments of diagnosis and assessment in functional dyspepsia (FD) patients. Among the subgroups of FD, postprandial distress syndrome (PDS) is related to gastric motility disorder.Methods Ten patients with FD and particularly with PDS as well as 10 healthy controls were enrolled in the study from September to November 2015. The gastric emptying shown as the half-life of gastric volume (T1/2) was measured by ultrasonography. The severities of spleen qi deficiency and dyspepsia symptoms were assessed by a spleen qi deficiency questionnaire (SQDQ) and the Nepean Dyspepsia Index-Korean version (NDI-K), respectively. In addition, a food retention questionnaire (FRQ), a damum questionnaire (DQ), a cold and heat questionnaire (CHQ), a deficiency and excess questionnaire (DEQ), and a visual analogue scale (VAS) of distention and fullness were completed by every participant.Results In comparison with the control group, the FD group showed significantly higher scores for the SQDQ, NDI-K, FRQ, DQ, DEQ, and VAS of distention and fullness. T1/2 was also significantly higher in the FD group than in the control group. There were significant correlations between T1/2 and the SQDQ score. However, there were no significant correlations between T1/2 and other questionnaire scores except for one item of the NDI-K.Conclusions According to these findings, it was determined that measuring gastric emptying using ultrasonography could be a quantitative indicator to diagnose spleen qi deficiency in FD patients.