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A tunable all-fiber optical attenuator (AOA) based on microfiber with adjustable coupling angle is reported and demonstrated. The AOA is fabricated of a microfiber probe coupled to a tapered fiber on the waist region through van der Waals and electrostatic forces. The attenuation can be tuned by adjusting the coupling angle of the two microfibers. When the coupling is fabricated of angles adjust from 8 0 o to 1 0 o , the optical attenuation can be tuned in a large range from 5.7 dB to 40.1 dB with low insertion loss. The simulation and experimental show that the coupling length can be changed by increasing the coupling angle, which results in decreasing the attenuation of AOA. The attenuation of AOA is decreased linearly by increasing the coupling angle. It provides a feasible approach to achieve attenuators with miniature volume, low cost, and multiple functions in optical communication and fiber lasers. • The AOA is fabricated by a microfiber probe coupled to a tapered fiber on the waist region through van der Waals and electrostatic force. • The optical attenuation can be linearly tuned in a large range with low insertion loss by adjusting the coupling angles. • The all-fiber structure of AOA excludes a difficult alignment between end-faces of two fibers and includes an easy connection to SMFs. • The AOA has the advantages of miniature volume, low cost, and multiple functions. [ABSTRACT FROM AUTHOR]