This research is aimed to explain the effect of ‘Jolly Phonics Lessons’ mobile application in order to overcome fifth grade students’ pronunciation problem of SDN Panggung Kidul Semarang. This study employed quantitative method. The research design is Quasi experimental research with 2 classes as the sample, 26 students of 5A perform as the experimental group, and the other 26 from 5B is the control group. The sample is chosen by purposive sampling technique. The research starts by conducting a try-out test to measure test item’s validity, followed by pre-test to measure students’ initial pronunciation ability, then giving treatment for both classes, and providing post-test to find out students’ pronunciation improvement. The data obtained are analyzed statistically by using SPSS application to find out the descriptive statistics, the score of normality test, paired samples test, homogeneity test, and independent sample test (hypothesis test). The hypothesis test (Independent Samples Test) shows that the Sig. (2-tailed) value obtained is 0,000 (<0,05), which indicates that Ha is accepted, and Ho is rejected. In other words, there is a significant difference in the average of pronunciation of students taught by using ‘Jolly Phonics Lessons’ Application and those taught by conventional method. Therefore, the researcher comes to a conclusion that ‘Jolly Phonics Lessons’ Application is more effective than conventional method to improve students’ pronunciation.