Surface/interfacial engineering is an essential technique to explore the fiber materials properties and fulfil new functionalities. An extensive scope of current physical and chemical treating methods is reviewed here together with a variety of real‐world applications. Moreover, a new surface/interface engineering approach is also introduced: self‐assembly via π–π stacking, which has great potential for the surface modification of fiber materials due to its nondestructive working principle. A new fiber family member, metal‐oxide framework (MOF) fiber shows promising candidacy for fiber based wearable electronics. The understanding of surface/interfacial engineering techniques on fiber materials is advanced here and it is expected to guide the rational design of future fiber based wearable electronics.