Due to the limited time allocated to English language instruction in school settings, it is worth examining how out-of-class activities can enhance second language (L2) learning. With the greater availability of online English resources, there has been increasing research examining the effects of exposure to English video materials on incidental language learning. However, most research has focused on the effects of a limited amount of viewing exposure and in-class or supervised viewing. Thus, the present experimental study investigates the effects of extended out-of-class viewing of TV series in three different input modes (captions, subtitles, no subtitles) on L2 learners' incidental vocabulary and listening comprehension development. Fifty L1 Chinese university students learning English as a foreign language were divided into three condition groups. A pre- and post-test design was used to measure vocabulary and listening comprehension development. The findings suggest that watching TV series with subtitles and captions may be beneficial for vocabulary acquisition, with the effect being stronger for the caption mode, whereas listening skills might improve when watching TV series without any subtitles. The study offers implications for English language instructors as well as for learners wishing to improve their vocabulary and listening comprehension skills incidentally.