The objectives of this research were to study allowance for doubtful accounts,Lending, quality of earnings, relationship between allowance for doubtful accounts andquality of earnings, and control with bank size. The data was collected from theannual financial statements of listed companies in the banking sector during the years2003 to 2007. Analyzed by fundamental statistics and correlation coefficients. Theresults indicated that from 2003 to 2007, 7 banks had decreases in allowance fordoubtful accounts, 8 banks had increases in lending, 10 banks had to set allowancefor doubtful accounts higher than Bank of Thailand criterion, indicated that banksetting up the allowance for doubtful accounts based on Prudent Banking Practiceand enough for damage from non-performing loan or NPLs, the most bank had to setallowance for doubtful accounts based on account receivable classification for class oflower standard, class of doubtful, class of bad debt, indicated that bank mightopportunistically reduce NPLs. In addition, 10 banks had non-smoothers in quality ofearnings ratio and there are no significant relationship between allowance for doubtfulaccounts and quality of earnings (p > 0.05).