Multifunctional skin-like sensors play an important role in next-generation healthcare, robotics, and bioelectronics. Here, we report a skin-like wearable optical sensor (SLWOS) enabled by a stretchable, flexible, and attachable patch embedded with an optical micro-/nanofibre (MNF), which is highly compatible with human skin, a curved surface, or cloth. Based on the transition from radiation modes into guided modes around the bending area of the MNF, the SLWOS embedded with a wavy MNF is highly sensitive to weak strain, achieving a gauge factor as large as 675 (strain <1%). The flexible SLWOS is also capable of monitoring the bending angle in a broad dynamic range with tunable sensitivity. In addition, temperature measurements in the range of -20 to 130 °C are realized by taking advantage of PDMS's large negative thermo-optic coefficient. The superior sensing performance together with mechanical flexibility enables the real-time monitoring of respiration, arm motion, and body temperature. This SLWOS will have great potential in wearable optical devices ranging from ultrasensitive sensors to photonic healthcare devices.