Soot formation of acetylene mixtures diluted with argon was studied behind reflected shock waves by monitoring attenuation of a laser beam in visible(632.8 nm) region of the spectrum. Experiments were conducted in the range of 1500~3800 K for temperatures, in the range of 0.6~3.3 atm for reflected shock pressures. During the pyrolsis of acetylene, a bell-shaped dependences of soot growth rate, induction time and soot yield were observed. At the same temperature range, an increase in total pressure made induction time short and soot growth rate shifted to lower temperature. Soot growth rate was also proportional to initial concentration of acetylene and they had the maximum value in the temperature range of 2000~2100 K.