The primary aim of this study was to open up new ways with which teachers could help learners improve their knowledge of vocabulary via collocation activities. This study investigated the effect of collocation activities on Iranian intermediate EFL learners’ vocabulary knowledge in order to solve their vocabulary problems. To this end, 60 female students from Pardis Institute in Lahijan, Iran participated in this study. They were divided into two groups of 30, one as an experimental group that received collocation activities as the treatment and a control group which received traditional method of vocabulary instruction. The researchers used a quasi-experimental, pre-test/post-test control group design. The data were analyzed using an Independent Samples T-test and a series of paired Samples T-tests. The findings of this study showed that collocation activities improved significantly participant learners’ vocabulary knowledge. The findings from paired-sample t-test indicated that the learners in the experimental group outperformed the control group in vocabulary knowledge.