A spike assembly for sport shoes includes a base with a tubular portion. A plurality of protrusions extends from the base portion in an axial direction of the base portion. Each protrusion includes an inclined side and a vertical side with a rounded portion connecting between the inclined side and the vertical side. A spike member includes a screw portion which is securely connected to the tubular portion, and a plurality of blocks extends from the spike member. Each block includes a curved protrusion facing the screw portion. The screw portion is connected to the tubular portion, and the curved protrusions are guided along the inclined sides of the protrusions and then, are stopped by the vertical sides of the protrusions. The spike member does not become loose by the weight of the wearer.