Table of Contents

Exhibit31.1

CERTIFICATION PURSUANT TO SECTION 302 OF THESARBANES-OXLEY ACT OF 2002

I, William H. Joyce,certify that:

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| 1.  | I have reviewed thisquarterly report on Form 10-Q of Nalco HoldingCompany; |

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| 2.  | Based on my knowledge,this report does not contain any untrue statement of material fact oromit to state a material fact necessary to make the statements made, inlight of the circumstance under which such statements were made, notmisleading with respect to the period covered by thisreport; |

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| 3.  | Based on my knowledge, thefinancial statements, and other financial information included in thisreport, fairly represent in all material respects the financialcondition, results of operations and cash flows of the registrant, asof, and for, the periods presented in thisreport; |

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| 4.  | The registrant’sother certifying officer and I are responsible for establishing andmaintaining disclosure controls and procedures (as defined in ExchangeAct Rules 13a-15(e) and 15d-15(e)) and internal control over financialreporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f))for the registrant andhave: |

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|  | (a)  | Designed such disclosurecontrols and procedures, or caused such disclosure controls andprocedures to be designed under our supervision, to ensure thatmaterial information relating to the registrant, including itsconsolidated subsidiaries, is made known to us by others within thoseentities, particularly during the period in which this report is beingprepared; |

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|  | (b)  | Designed suchinternal control over financial reporting, or caused such internalcontrol over financial reporting to be designed under our supervision,to provide reasonable assurance regarding the reliability of financialreporting and the preparation of financial statements for externalpurposes in accordance with generally accepted accountingprinciples; |

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|  | (c)  | Evaluated theeffectiveness of the registrant’s disclosure controls andprocedures and presented in this report our conclusions about theeffectiveness of the disclosure controls and procedures, as of the endof the period covered by this report based on such evaluation;and |

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|  | (d)  | Disclosed in this reportany change in the registrant’s internal control over financialreporting that occurred during the registrant’s most recentfiscal quarter that has materially affected, or is reasonably likely tomaterially affect, the registrant’s internal control overfinancial reporting; and |

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| 5.  | Theregistrant’s other certifying officer and I have disclosed,based on our most recent evaluation of internal control over financialreporting, to the registrant’s auditors and the audit committeeof the registrant’s board of directors (or persons performingthe equivalent functions): |

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|  | (a)  | Allsignificant deficiencies and material weaknesses in the design oroperation of internal control over financial reporting which arereasonably likely to adversely affect the registrant’s abilityto record, process, summarize and report financial information;and |

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|  | (b)  | Any fraud, whether or notmaterial, that involves management or other employees who have asignificant role in the registrant’s internal control overfinancial reporting. |

Date: May  10,2006

/s/ WILLIAM H.JOYCE                        Name:    WilliamH. JoyceTitle:     Chairman and Chief ExecutiveOfficer

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