Exhibit31.1

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

I, William H. Joyce, certifythat:

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| 1.  | I have reviewed this annual report on Form10-K of Nalco Holding Company; |

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| 2.  | Based on myknowledge, this report does not contain any untrue statement of amaterial fact or omit to state a material fact necessary to make thestatements made, in light of the circumstance under which suchstatements were made, not misleading with respect to the period coveredby this report; |

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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’s other certifyingofficer and I are responsible for establishing and maintainingdisclosure controls and procedures (as defined in Exchange Act Rules13a-15(e) and 15d-15(e)) and internal control over financial reporting(as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for theregistrant and have: |

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| (a)  | Designed suchdisclosure controls and procedures, or caused such disclosure controlsand procedures 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 such internal controlover financial reporting, or caused such internal control overfinancial reporting to be designed under our supervision, to providereasonable assurance regarding the reliability of financial reportingand the preparation of financial statements for external purposes inaccordance with generally accepted accountingprinciples; |

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| (c)  | Evaluated the effectiveness ofthe registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period coveredby this report based on such evaluation;and |

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| (d)  | Disclosed in this report any change inthe registrant’s internal control over financial reporting thatoccurred during the registrant’s most recent fiscal quarter (theregistrant’s fourth fiscal quarter in the case of an annualreport) that has materially affected, or is reasonably likely tomaterially affect, the registrant’s internal control overfinancial reporting; and |

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| 5.  | The registrant’sother certifying officer and I have disclosed, based on our most recentevaluation of internal control over financial reporting, to theregistrant’s auditors and the audit committee of theregistrant’s board of directors (or persons performing theequivalent functions): |

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| (a)  | All significantdeficiencies and material weaknesses in the design or operation ofinternal control over financial reporting which are reasonably likelyto adversely affect the registrant’s ability to record, process,summarize and report financial information;and |

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| (b)  | Any fraud, whether or not material,that involves management or other employees who have a significant rolein the registrant’s internal control over financialreporting. |

Date: March  2,2006

/s/ William H.Joyce                                                    Name:  WilliamH. JoyceTitle:      Chairman and Chief ExecutiveOfficer

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