The aim of this study is to determine the effect of word clustering method on vocabulary learning of Iranian EFL learners through a case of semantic versus phonological clustering. To this effect, 80 homogeneous students from four intermediate classes at an English institute in Torbat e Heydariyeh participated in this research. They were assigned to four groups according to semantic versus phonological clustering [± semantic, ± phonological] then, based on each groups' clustering pattern, 10 selected words were taught. At the end of the treatment phase, immediate and delayed posttests of vocabulary were given to students in a multiple choice format to understand the effects of word clustering in short and long term vocabulary learning. The analysis of the research was done in SPSS through one-way ANOVA. The results in both immediate and delayed post-tests showed a statistically significant difference among groups. The obtained mean scores revealed this rank order of mean performance in both immediate and delayed post-tests: [+ semantic, + phonological], [+ semantic, - phonological], [- semantic, + phonological], and [- semantic, - phonological]. Additionally, the effect of time did not turn out to be significant. These findings and relevant implications are discussed in the paper.
