It is 0.6666 (6 repeated infinitely, usually shown as 0.66, with a bar notation above the 6) Typically this is rounded to either 0.67 or 0.667.
http://wiki.answers.com/Q/What_is_the_decimal_for_...

Two thirds as a fraction is a repeating decimal. The answer is
http://www.chacha.com/question/whatistwothirds...

To figure out what is one half of two thirds I convert it to decimals. Two thirds is .666 and 1/2 is .5. Then I take .666 and multiply it by .5. The answer is .333 or 1/3.
http://www.ask.com/webanswers/Health/Diseases/wha...

Twothirds as a decimal is 0.66666. Text us again soon!!
http://www.kgbanswers.com/whatistwothirdsasad...
