This study was conducted to investigate the treatment of wastewater from acetaldehyde manufacturing plant by activated sludge process with Micrococcus roseus AW-6, Micrococcus luteus AW-22, Microbacterium lacticum AW-38 and Microbacterium laevaniformans AW-41. The COD_Mn and BOD_5 of the wastewater were 5,260㎎/L and 6,452㎎/L, respectively. pH was 1.85. The main organic component in the wastewater was acetic acid which was contained 67,600㎎/L. Optimum dilution time for activated sludge process was shown 10 times. The specific substrate removal rate(K_e) was 1.95day^-1 and the nonbiodegradable matters(S_n) were 23.2㎎/L. Saturation constant (K_e) and maximum specific growth rate(q_max) were 1,640㎎/L and 2.33day^-1, respectively. Sludge yield coefficient(Y) and endogenous respiration coefficient(K_d) were 0.28㎎ MLVSS/㎎COD and 0.02day^-1, respectively. COD_cr removal efficiency was 91% for 1.95day of hydraulic retention time.