Vocabulary has always played an important role in language learning and there has been several strategies to learn it. Among the ways of vocabulary learning, incidental vocabulary learning has recently been in center of attention. In this field, the effect of input modes on incidental vocabulary learning has been investigated since last century; however; not much research has been dedicated to it. This study investigates the possible effect of input modes on incidental vocabulary learning and tries to determine the extent to which each input mode contributes to incidental vocabulary learning. A sample of 89 Iranian young female students from English language institutes in Zanjan province was selected to this end. They were assigned to four groups, including three experimental groups and one control group. All the groups participated in a 14-day procedure (three sessions) of study including VLT, pretest, immediate posttest, and delayed posttest, but only experimental groups received a short story as the treatment in different input modes including reading, listening, and reading while listening. The tests included a checklist and a multiple-choice to measure the incidental vocabulary learning of participants. Participants also completed a Vocabulary Level Test (Webb et al., 2017). Several one-way ANOVAs were conducted to analyze the checklist and multiple-choice tests. The results indicated that the differences between input modes in terms of incidental vocabulary learning was in favor of the Reading while Listening mode and, to a lesser degree, the Reading mode. However, only the Reading while Listening mode resulted in Vocabulary retention. The data showed a very little (almost no) advantage in favor of the Listening mode. These findings can have implications for teachers, learners, and material developers.
