Bioaugmentation　was　investigated　as　a　method　to　accelerate　the　recovery　of　an　anaerobic　sequencing　batch　reactor　(ASBR)　exposed　to　the　organic　shock　load.　Two　sets　of　ASBRs　were　subjected　to　double　organic　load　that　influent　chemical　oxygen　demand　(COD)　concentrations　were　increased　from　4,000　+/-　100　to　8,000　+/-　150　mg　L-1　for　a　week.　Bioaugmented　reactor　received　the　enriched　butyric　acid-utilizing　syntrophic　culture　(10%　w/w)　and　evolutions　of　microbial　community　were　analyzed　by　a　quantitative　polymerase　chain　reaction.　Aftershock　load,　the　performance　of　acidification　was　attained　with　the　effluent　COD　concentrations　increased　from　70　to　5,300　mg　L-1　and　pH　decreasing　from　7.1　to　5.1　approximately　in　two　reactors.　Smithella　was　badly　inhibited　by　the　VFAs　accumulation　and　high　H-2　partial　pressure.　Bioaugmented　reactor　achieved　significantly　less　time　to　recover　than　the　non-bioaugmented　reactor,　40　and　110　d　respectively.　The　rapid　recovery　for　the　bioaugmented　reactor　was　mainly　attributed　to　the　added　microorganisms　containing　a　large　number　of　Methanobacteriales　and　Syntrophomonas,　released　the　feed-back　inhibition　and　resulted　in　a　rapid　recovery　of　Smithella,　thus　accelerated　the　degradation　of　propionic　acid.　Therefore,　bioaugmentation　is　a　promising　approach　for　promoting　the　recovery　of　the　acidified　anaerobic　reactors　caused　by　the　organic　shock　load.