With the rapid development of Augmented Reality (AR), an increasing number of studies has been conducted to explore the effectiveness of this technology in the field of education. Few, however, have examined how AR might influence EFL (English as a Foreign Language) learners’ vocabulary learning efficiency. To fill in this gap in the literature, the purpose of this study is to compare traditional English flash cards with the vocabulary learning method of Augmented Reality to see which English vocabulary learning is more efficient for elementary school students. The study was conducted at an elementary school in Taiwan, and the participants were 66 third grade pupils in total. The study was conducted at two stages in terms of data collection. At the first stage, the control and experimental groups took the same English vocabulary test without any teacher instruction as a pretest. At the second stage, the control group used flashcards to learn 20 target English words by themselves in 30 minutes. The experimental group adopted the Augmented Reality 3D effect of 20 target words by themselves in 30 minutes. After that, both groups took the same English vocabulary test again as a posttest. On the whole, Augmented Reality teaching effects apparently excel the effects of the traditional vocabulary learning methods. The results of this study have shown that the learning method of Augmented Reality was more efficient than the learning method using English flash cards at various proficiency levels (high, intermediate, and low) in terms of English vocabulary learning. The learning method of English flash cards had significant differences in high and low level groups as well as intermediate and low level groups, with the exceptions of high and intermediate level groups. It is worth improving children’s English vocabulary learning by using Augmented Reality in their daily lives in terms of mobile learning.