In present study, the effect of red blood cells concentration on the clot viscoelastic properties was assessed by acoustic radiation force technique in vitro. The experiments were performed on porcine whole blood with different hematocrits from 0 to 40%. Clot formation was induced by adding 2 ml of 0.5 M CaCl2 solution into a 20-ml blood sample. The viscoelastic properties of clot were estimated by detecting the displacement of a solid sphere within clot in response to the applied acoustic radiation force. In experimental system, the solid sphere was pushed by a 1 MHz single element focused transducer. Another single element focused transducer with a center frequency of 20 MHz was used to track the displacements of sphere. For each clot sample, acoustic radiation force tone bursts of 0.25 ms to 7 ms are applied in consecutive experiments. The spatio-temporal behavior of the displacement of sphere was used to assess the viscoelastic properties of clot (with different hematocrits). The experimental result indicates that the value of shear modulus of blood clot decreased from 585±127 Pa at plasma to 168±26 Pa at 40% hematocrit. This result can be used to explain that the concentration of fibrinogen plays the major role in clot elastic properties. In addition, the viscoelastic properties of blood clot can be assessed using a temporal behavior rather than a spatial approach.