This study investigated the effectiveness of incidental focus on form in promoting second language development in text-based live chats. Sixteen college-level Taiwanese English language learners were partnered with American college students to complete two communicative tasks via synchronous chats on Instant Messenger. Language-related episodes (LREs) were identified and used as a basis for individualized test items in which the participants' linguistic issues were addressed and recalled. The results of two posttests revealed that focus on form in text-based live chats was highly associated with subsequent second language development. Successful uptake and type of feedback were two major factors for learners' accurate grammatical and lexical knowledge recall, which serve as pedagogical guidelines to promote noticing in second language development.