Abstract: An atomic force microscopy (AFM) based hanging fiber probe is developed to investigate contact line dissipation. A universal scaling law, ξ = απdη, is obtained for various liquids (and soap films) of viscosity η and glass fibers of diameter d with different surface chemistries. The proportionality constant α is found to be α = 0.8 ± 0.2, independent of the contact angle and surface tension. The AFM system is also used to study wetting transition and contact angle hysteresis at a DPPC-monolayer interface.