You can withdraw (or redeem) your fund units, anytime you want. But remember that if you redeem your units within ONE year of investment than it will attract Short Term Capital Gain tax. It will be levied on the profit made by you in that fund since you invested.This tax is applicable only if you redeem within ONE year of investment in that fund.

All fund companies allow investors with withdraw there money anytime they want to EXCEPT if the investment is made in a TAX SAVING MUTUAL FUND(ELSS) or in a CLOSED ENDED MF.

IF YOU HAVE INVESTED IN A TAX SAVING MF THEN YOU CAN ONLY WITHDRAW AFTER 3YEARS FROM THE DATE OF INVESTMENT.