Please read this

Fixed or Determinable Annual or Periodical Income (FDAP)
FDAP income is all income except:

Gains from the sale of property (including market discount and option premiums but not including original issue discount), and

Items of income excluded from gross income without regard to U.S. or foreign status of the owner of the income, such as tax-exempt municipal bond interest and qualified scholarship income.


The following items are examples of FDAP income.

Compensation for personal services.

Dividends.

Interest. ....


IF you paid the following type of income: THEN you generally must withhold at the following rate:
Taxable part of U.S. scholarship or fellowship grant paid to holder of “F”“J”“M” or “Q” visa (see Scholarship and Fellowship Grants, later) 14%
Gross investment income from interest, dividends, rents, and royalties paid to a foreign private foundation 4%
Pensions—part paid for personal services (see Pensions, Annuities, and Alimony, later) Graduated rates in
Circular A or Circular E
Wages paid to a nonresident alien employee (see Pay for Personal Services Performed, later) Graduated rates in
Circular A or Circular E
Each foreign partner's share of effectively connected income of the partnership (see Partnership Withholding on Effectively Connected Income, later) 35%
Distributions of effectively connected income to foreign partners by publicly traded partnerships (see Publicly Traded Partnerships, later) 35%
Dispositions of U.S. real property interests (see U.S. Real Property Interest, later) 10% *
Dividends paid to Puerto Rico corporation 10%
All other income subject to withholding 30%

*35% in the case of certain distributions by corporations, partnerships, trusts, or estates.

資料來源
http://www.irs.gov/publications/p515/ar02.html#en_US_publink100057302