The purpose of the study on Knowledge and Understanding of Personal Income Tax Planning is to study the knowledge and understanding on personal income tax problems and obstacles of individual taxpayers regarding internet tax filing. The study compared the level of knowledge understanding and planning of personal income tax of the sample with different demographic factors. The questionnaire was used as a tool to collect data. A total of 410 samples were used for one-way analysis of variance (One Way ANOVA) and compared by Least-Significant Different (LSD). The research found that the overall understanding of personal income tax planning was moderate. The most knowledgeable issues were net income taxable income expenses and tax reduction which were in high level. Secondly the issue of “the personal income tax rate is a progressive tax rate” was in a very high level. The lowest level was “each type of assessment has different deduction rates”. “Type 1 income has the least expense deductible rate” was in moderate level. In conclusion different gender occupation and education levels have statistically significant knowledge and understanding on tax planning.