This study examined if gaze-contingent textual enhancement could be used as an interactive focus-on-form device to promote learning of second language (L2) collocations from computer-mediated reading tasks. Seventy-five Chinese ESL users read three English texts that contained twelve target collocations, presented under one of three conditions: no highlighting, proactive highlighting (target collocations highlighted in advance), and gaze-contingent highlighting (target collocations highlighted when looked at). Participants' eye movements were captured during the reading task, and collocation form recall and recognition tests were administered immediately after and 2 weeks later. Additionally, five participants from each group took part in a stimulated recall session, eliciting their thoughts while reading. The results indicated that both highlighting techniques increased total fixation duration and count on the target collocations and improved collocation form recall and recognition scores in the posttests. Gaze-contingent highlighting demonstrated a more durable impact on the collocation recall test compared to proactive highlighting. The stimulated recall comments also revealed that gaze-contingent highlighting tended to promote attentive processing of the target collocations. These findings suggest that highlighting is a useful focus-on-form technique in task-based reading contexts, with gaze-contingent highlighting yielding potential benefits in terms of L2 collocation learning.