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Indicate by check mark whether the registrant by furnishing the
information contained in this Form is also thereby furnishing the
information to the Commission pursuant to Rule 12g3-2(b) under
the Securities Exchange Act of 1934.

Yes ______ No ___X___

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COMPANHIA DE SANEAMENTO BÁSICO DO ESTADO DE SÃO PAULO – SABESP

Publicly-held Company
Corporate Taxpayer’s ID (CNPJ) 43.776.517/0001 -80
Corporate Registry ID (NIRE) 35.300.016.831
Rua Costa Carvalho n° 300

MATERIAL FACT

Companhia de Saneamento Básico do Estado de São Paulo – Sabesp (“SABESP” or “Company”), pursuant to the provisions of Instruction 358, of January 3, 2002, of the Brazilian Securities and Exchange Commission (“CVM”), as amended, hereby informs its shareholders and the market in general that SABESP’s Board of Directors, at a meeting held on November 5, 2009, approved the 4th issue of promissory notes of the Company, for public offering, on a firm commitment and restricted efforts placement basis, pursuant to CVM Instruction 476, of January 16, 2009 (“CVM Instruction 476”), in the total amount of nine hundred million reais (R$900,000,000.00) (“Promissory Notes” and “Offering”).

The Promissory Notes’ maturity term shall be one hundred and eighty (180) days, as of its issue date, and the funds raised by the Company through the promissory notes’ payment shall be allocated for settling the 3rd issue of promissory notes, in the amount of six hundred million reais (R$600,000,000.00), as well as for settling other financial commitments and enforcing the Company’s budget.

The structuring and distribution process is being conducted by the pool of financial institutions under the leadership of BB-Banco de Investimento S.A. (“BB-BI” or “Lead Coordinator”), also having as coordinators Caixa Econômica Federal (“CAIXA”), HSBC Corretora de Títulos e Valores Mobiliários S.A. (“HSBC”) and Banco Votorantim S.A. (“Votorantim” and, jointly with the Lead Coordinator, CAIXA and HSBC, “Coordinators”).

The Promissory Notes shall be paid with funds to be raised by the Company through a public issue of Debentures, which is currently being structured by the Coordinators on a firm commitment basis, pursuant to CVM Instruction 400.

São Paulo, November 23, 2009.

Rui de Britto Álvares Affonso
Chief Financial and Investor Relations Officer

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This press release may contain forward-looking statements. These statements are statements that are not historical facts, and are based on management's current view and estimates of future economic circumstances, industry conditions, company performance and financial results. The words "anticipates", "believes", "estimates", "expects", "plans" and similar expressions, as they relate to the company, are intended to identify forward-looking statements. Statements regarding the declaration or payment of dividends, the implementation of principal operating and financing strategies and capital expenditure plans, the direction of future operations and the factors or trends affecting financial condition, liquidity or results of operations are examples of forward-looking statements. Such statements reflect the current views of management and are subject to a number of risks and uncertainties. There is no guarantee that the expected events, trends or results will actually occur. The statements are based on many assumptions and factors, including general economic and market conditions, industry conditions, and operating factors. Any changes in such assumptions or factors could cause actual results to differ materially from current expectations.

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