A spring chuck having a locking mechanism provided between two handles of the spring chuck. The locking mechanism includes a sleeve connected at an end to one handle of the chuck, a shaft having an end connected to another handle of the chuck and another end movably located in the sleeve via a lower open end thereof, a brake handle having a ring-shaped head put around the shaft and pivotally connected the lower open end of the sleeve, and a compression spring mounted around the shaft between the sleeve and the ring-shaped head of the brake. The compression spring normally pushes the ring-shaped head to pivotally turn away from the sleeve to frictionally contact with the shaft, preventing the shaft from moving in the sleeve and thereby lock the handles of the chuck to a fixed position. Pushing the brake handle toward the sleeve causes the ring-shaped head to align with the sleeve without frictionally contacting with the shaft and therefore allows the handles of the chuck to move freely.