Most advanced humidity sensors of present days are based on the techniques dependent on the external power supplies that require periodic charging and replacement, causing additional cost and complicated management issues to the humidity-sensing systems. In this work, this problem has been overcome through a fundamental approach based on triboelectric contact electrification between a pair of the as-fabricated highly functional materials. The concept of self-powered humidity detection with an ultrafast response and relaxation times has been successfully demonstrated by introducing a triboelectric humidity sensor (TEHS) based on hydrophobic micro-/nano-textured polydimethylsiloxane and nano-textured aluminum films. The proposed humidity sensor produces an electric output for an external mechanical force that is readily related to the relative humidity (% RH) level over a wide range of ambient conditions. The as-fabricated TEHS device shows a record-fast response time and a relaxation time of 2.2 s and 1.9 s, respectively, and has very good linearity in electric output performance in a wide humidity detection range of 10–90% RH. The proposed device possesses a highly reliable/stable output performance, which is essentially constant over thousands of contact–separation stability test cycles. Moreover, in comparison to a battery-powered commercial humidity sensor adopted in this work, the self-powered TEHS device shows a significantly better performance in terms of response time and relaxation time. Therefore, this work paves the way toward the practical implementation of the triboelectric effect-enabled self-powered humidity sensors.