The utility model provides a derailleur breather plug structure and derailleur, wherein, derailleur breather plug structure is provided with the air vent including the cock body and the gag of ventilating of ventilating on all laterads of the one end of the cock body of ventilating, and the central line of air vent is greater than 0 with the contained angle of the axis of cock body of ventilating and just is lighter than 90, the inside shape of gag of ventilating and the outside shape looks adaptation of the other end of the cock body of ventilating. The utility model provides a derailleur breather plug structure just is lighter than 90 because the contained angle between the axis of the central line of air vent and the cock body of ventilating is greater than 0 behind pneumatolytic oily condensing reflux to air vent. The oil that makes the condensation air vent that can flow very fast under the action of gravity is favorable to oily backward flow to can effectively avoid the oil leak, make the structure of derailleur breather plug structure more reasonable.