An anti-slip device for the supporting stand of a monitor, which is capable of preventing the bottom rod of the supporting stand from slipping. The anti-slip device includes: a semi section anti-slip sleeve; at least one insert member which protrudes from the anti-slip sleeve; a rotatable body cover which is integrally formed with and extends from one end of the anti-slip device; and a snap fastener which is connected to the free end of the body cover. An insertion slot is correspondingly formed on the anti-slip sleeve. To utilize the monitor, the anti-slip device is clamped onto the bottom rod of the supporting stand. The insert member is further inserted into the reserved hole in the bottom rod. The body cover is then closed around the top of the bottom rod. It is because of the insert connection to the insert member and the clamp by the body cover and the anti-slip sleeve, that the anti-slip device is securely attached to the supporting stand.