Natural fibers are a renewable resource that has become an economic alternative to replace synthetic fibers as reinforcement in composite materials. In this study, the aim was to characterize physical and thermal properties of the Andean Stipa obtusa and Jarava ichu leaves (grasses known as ichu) before and after the alkaline treatment. Energy dispersive spectrum identified external phytoliths on the surface of nontreated raw leaves. With the alkaline treatment, improvement on the thermal stability and increment in the crystalline index and size was observed. Additionally, raw leaves present a hydrophobic behavior; however, with the treatment this hydrophobicity was lost for Stipa obtusasignificantly but not for the Jaravaichu. Furthermore, low surface energy was observed for the nontreated raw leaves and increasing consistently for the treated fibers. According with these results, these grasses are quite interesting materials from which fibers can be extracted for engineering applications such as composite materials. © 2019 Taylor & Francis.