Using the observed asymmetry parameters (arm-length ratio (Q) and apparent flux ratio (R)) usually observed at kilo parsec region and the observed apparent expansion speed (ï¢ï¡) of the components seen with the parsec regions of jets of radio sources, we obtained an analytical expression that allowed us to constrain the Lorentz factor of jet in hotspots of extragalactic radio sources. Our result indicates that relativistic bulk motion persists even in the kilo parsec regions of hotspots of extragalactic radio sources. The average value of the estimated Lorentz factor of ï¨ï§ï©~12 ± 6 was obtained using the arm-length ratio. For sources with observed apparent flux ratio (R), the estimated average Lorentz factor is ï¨ï§ï©~15 ± 8. Correlation analysis indicates that the estimated bulk speed is independent of extended luminosity (P) and source projected linear size (D).