Commodities Exchange Improvements Act of 2005

Commodities Exchange Improvements Act of 2005 - Amends the Commodity Exchange Act to include natural gas as an agricultural commodity within the purview of the Act, including hybrid instruments based upon natural gas.

States that an agreement, contract, or transaction involving natural gas may not be exempted from the regulatory requirements of the Act.

Prohibits a board of trade that is a designated contract market from changing, without prior Commodity Futures Trading Commission (CFTC) approval, a rule, regulation, or contract specification that applies to any agreement, contract, or transactions involving natural gas.

Requires back-up reporting of large positions as prescribed by the CFTC in order to deter manipulation of the price of contracts of sale of natural gas for future delivery.

Directs the CFTC to prescribe rules requiring any board of trade to implement rules that provide for any contract of sale for future delivery of natural gas to be settled in cash in lieu of making delivery of the natural gas in circumstances in which the CFTC has determined that market conditions suggest possible manipulation.

Subjects commodity price manipulation to a civil penalty.

Prohibits, for one year, CFTC members from working for any organization subject to Commission regulation.