The current study attempted to examine the effect of collaborative tasks via incidental attention on vocabulary enhancement, reading comprehension skill and vocabulary learning motivation. To this purpose, 90 male and female intermediate level English learners at the English language institute of Atieh Gharb in Sanandaj with their age ranging from 15 to 19 were chosen for this study. The study was done by using experimental research design. This design was often used in classroom experiments when two experimental and one control groups were such naturally assembled groups as three classes, which were made homogenous. The results showed that there was a significant difference between experimental groups and control group such that the learners of the two experimental groups who had been taught through collaborative learning method performed better than those learners of the control group who had been taught vocabulary through traditional approach. Also, the learners of the experimental group I outperformed the learners of experimental group II. The findings of the immediate and delayed vocabulary post-tests indicated that the learners of experimental groups outperformed the control group both in immediate and delayed post-tests, it means that the motivation of vocabulary learning in experimental groups was higher than control group. Moreover, the motivation of vocabulary learning in experimental group II was lower than experimental group I. Besides, a further analysis known as the post hoc Tukey-HSD test was conducted to pinpoint exactly where the differences exist among the mean of three groups on immediate post-test.