The purpose of this study was to examine whether a gratitude training program for preservice dental hygienists affects their gratitude disposition, self-esteem, and happiness. Dental hygiene students were recruited from a college in D and administered a pretest. The 76 selected participants were primarily those who had never written a gratitude journal. Participants were then randomly divided into an experimental group and a control group. Three participants failed to complete the program, leaving 73 subjects in the final analysis. Data were analyzed using the χ² test, independent sample t-test, and analysis of covariance. The mean gratitude disposition score improved from 31.11±5.55 in the pretest to 34.41±4.38 in the posttest in the experimental group and from 31.44±4.41 to 32.06±4.63 in the control group. The mean self-esteem score improved from 31.22±4.03 to 33.16±3.44 in the experimental group and from 30.53±4.42 to 30.97±3.80 in the control group. The mean happiness score improved from 19.54±2.64 to 21.78±2.43 in the experimental group and from 19.64±3.32 to 20.08±2.91 in the control group. All of the participants improved their gratitude disposition, self-esteem, and happiness scores while participating in the gratitude training program, and it is expected that if such positive emotions can be sustained, they will naturally acquire the basic requirements of dental hygienists and build a better vocational consciousness and a higher sense of duty, as well as have a further positive effect on the quality of dental medical service. Further studies should be conducted to propose a concrete plan to expand and operate this gratitude training program more effectively.