A pepper mill includes a driving member coupled rotatably to a container body and cooperating with the container body to define a receiving space, a grinding unit, a planetary gear mechanism, and an adjusting component. The grinding unit includes a coupling shaft extending rotatably and being movable in the receiving space, a stationary first grinding seat, and a second grinding seat co-rotatable with the coupling shaft. The size of a grinding space between the first and second grinding seats is adjusted when the coupling shaft and the second grinding seat move axially relative to the first grinding seat. The planetary gear mechanism includes a driving gear unit and a driven gear unit driven rotatably by the driving gear unit to drive rotation of the coupling shaft. The adjusting component is connected threadedly to the coupling shaft and is operable to drive the axial movement of the coupling shaft and the second grinding seat.