An in-ear earphone has a shell including an upper shell and a lower shell cooperating with the upper shell to define a resonance space for receiving a loudspeaker. A plurality of damping objects are made of different elastic and compressible materials. A group of first adjusting elements are capable of being replaceablely assembled to the lower shell for receiving external sound signals. Each first adjusting element defines a receiving fillister and a sound hole connected with the receiving fillister. Each first adjusting element has one damping object disposed in the receiving fillister and further disposed between the sound hole and the resonance space. A group of second adjusting elements are capable of being replaceablely assembled to the upper shell for transmitting the sound signals out. Each second adjusting element defines a receiving cavity for receiving one of the damping objects therein and makes it face to the resonance space.