Wearable　strain　sensors　are　arousing　increasing　research　interests　in　recent　years　on　account　of　their　potentials　in　motion　detection,　personal　and　public　healthcare,　future　entertainment,　man-machine　interaction,　artificial　intelligence,　and　so　forth.　Much　research　has　focused　on　fiber-based　sensors　due　to　the　appealing　performance　of　fibers,　including　processing　flexibility,　wearing　comfortability,　outstanding　lifetime　and　serviceability,　low-cost　and　large-scale　capacity.　Herein,　we　review　the　latest　advances　in　functionalization　and　device　fabrication　of　fiber　materials　toward　applications　in　fiber-based　wearable　strain　sensors.　We　describe　the　approaches　for　preparing　conductive　fibers　such　as　spinning,　surface　modification,　and　structural　transformation.　We　also　introduce　the　fabrication　and　sensing　mechanisms　of　state-of-the-art　sensors　and　analyze　their　merits　and　demerits.　The　applications　toward　motion　detection,　healthcare,　man-machine　interaction,　future　entertainment,　and　multifunctional　sensing　are　summarized　with　typical　examples.　We　finally　critically　analyze　tough　challenges　and　future　remarks　of　fiber-based　strain　sensors,　aiming　to　implement　them　in　real　applications.