The main purposes of this research are to investigate tax problems in operating businesses and test the effect of tax planning for sales promotion on tax performance efficiency of VAT registrant. Data were obtained from 272 accounting managers of VAT registered firms in Thailand by using questionnaires. The statistics used for analyzing data were frequency, percentage, mean, and standard deviation. While multiple correlation analysis and multiple regression analysis were used to test the hypothesis. The results show that 1) most tax problems encountered by businesses are regarding withholding tax (inaccurate amounts withheld); next is corporate income tax (unused tax-benefits); and last is value-added tax (received incorrect tax invoices). 2) Tax planning for sales promotion has a significant effect on tax performance efficiency. As a result, to achieve tax performance efficiency VAT registrants should aware of the important of taxation and tax planning for different kinds of sales promotions. They should also prepare relevant tax documents correctly and completely according to tax law in order to minimize tax burden and maximize tax benefits.