An adjusting device for a goggle strap is disposed at both ends of the strap for quick connection to two connecting ends of the goggle body. The adjusting device comprises a body, a locking shaft, a cover and two push buttons. The strap is rolled around the locking shaft. When the cover is closed, a protruding strip of the strap is engaged by an engaging rib of the cover. When pressing the push buttons passed through both sides of the body, the cover is opened outward, so as to adjust the length of the strap again.