The mechanical and biophysical properties of the individual tumor cell pseudopod protrusion under a chemotactic influence has been investigated. Experiments were performed on single A2058 melanoma cells activated by type IV collagen using in vitro micropipette manipulation. This method was used to study the kinetics and extent of pseudopod formation during tumor cell active micromotion. Microscope image shows that the protrusion takes place in two phases with an initial radially symmetric outpouching followed by an irregular shaped extension. The two-phase protrusion during pseudopod extension has raised new possible mechanisms of actin polymerization and osmotic flux which modulate the process of tumor cell micromotion. The simple biophysical model presented describes the relative roles of actin polymerization and interfacial osmosis in pseudopod formation.