The effect of variables on efficiency of $SO_2$ removal from a simulated waste gas by use of ammonia solution was studied. The variables were gas, feed solution, and recirculation flow rate, $SO_2$ concentration in the gas phase, $NH_3$ concentration in the feed solution, pH of scrubber effluent solutions. The scrubber was 3"-OD methyl metacrylate column packed with $\frac{1}{4}$"-plastic Rasching ring in 90-cm packed height. Solution analysis was performed by Palmrose method and Ph meter. The $SO_2$ removal efficiency increased slowly as feed solution and recirculation flow rates increased at constant gas velocity, while at constant feed solution and recirculation flow rates, the effect of gas flow rate on the efficiency was considerably small. The effect of gas, feed solution, and recirculation flow rates on $SO_2$ removal efficiency was obtained as follows; $$ \mbox{EFF}=8.27G^{0/0552}F^{0/118}R^{0/772}$$ The $SO_2$ removal efficiency increased with $SO_2$ concentration in the gas phase and $NH_3$ concentration in the feed solution. The effect of $SO_2$ concentration in the gas phase on the efficiency was higher than that of $NH_34 concentration in the feed solution. The $SO_2$ removal efficiency increased sharply as pH of scrubber effluent solution increased, and became almost constant when pH was above 6.5. The optimum pH range in this study was 6.5-6.9. Gas film mass transfer coefficient increased with increasing gas velocity in the conditions of constant feed solution and recirculation flow rates. The effect of gas and liquid flow rates on gas film mass transfer coefficient was obtained as follows; $$ k_G=1.94\times10^{-5}G^{1.16}L^{0.647}$$