Vocabulary learning is one of the crucial matters in second language learning. There is a vast body of research in this field which has been done by famous researchers around the world, but still there is no specific solution for extending lexical knowledge in the best way. Therefore, we have conducted a meta-analysis on a body of 30 research projects to investigate the usefulness of different strategies of vocabulary learning. The results showed that the strategies which are used by students are as follows in order: determination, cognitive, memory, meta-cognitive, and social strategies. Besides, it seems that guessing from context and using the dictionary are among the strategies which are most favored by successful students. In addition, the relationship between context, treatment, and methodology by vocabulary learning strategy were studied. It was clear that learners of different contexts would prefer different strategies, and teachers used specific strategies according to their syllabus. For further research, it is suggested to select a larger body of studies. It is advised to make teachers aware of the importance of choosing an appropriate strategy of vocabulary learning for language learners to pave the way of improving lexical knowledge for them.