Exhibit 32.1


                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002


In connection with the Annual Report of Kronos Worldwide,  Inc. (the Company) on
Form 10-K for the period ended  December  31, 2005 as filed with the  Securities
and Exchange  Commission on the date hereof (the Report),  I, Harold C. Simmons,
Chief  Executive  Officer of the  Company,  and I,  Gregory M.  Swalwell,  Chief
Financial Officer of the Company,  certify,  pursuant to 18 U.S.C. section 1350,
as adopted pursuant to section 906 of the Sarbanes-Oxley Act of 2002, that:

(1)  The Report fully complies with the  requirements  of section 13(a) or 15(d)
     of the Securities Exchange Act of 1934; and

(2)  The information  contained in the Report fairly  presents,  in all material
     respects, the financial condition and results of operations of the Company.




/s/ Harold C. Simmons
- --------------------------
Harold C. Simmons
   Chief Executive Officer


/s/ Gregory M. Swalwell
- --------------------------
Gregory M. Swalwell
   Chief Financial Officer


March 16, 2006

Note: The certification  the registrant  furnishes in this exhibit is not deemed
"filed" for purposes of Section 18 of the  Securities  Exchange Act of 1934,  as
amended,  or otherwise subject to the liabilities of that Section.  Registration
Statements or other documents filed with the Securities and Exchange  Commission
shall not incorporate this exhibit by reference,  except as otherwise  expressly
stated in such filing.