UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 13F FORM 13F COVER PAGE Report for the Calendar Year or Quarter Ended: March 31, 2008 Check here if Amendment [ ]; Amendment Number: _____ This Amendment (Check only one.): [ ] is a restatement [ ] adds new holdings entries. Institutional Investment Manager Filing this Report: Name: The Cincinnati Specialty Underwriters Insurance Company Address: 6200 South Gilmore Road Fairfield, Ohio 45014 13F File Number: 28-12741 The institutional investment manager filing this report and the person by whom it is signed hereby represent that the person signing the report is authorized to submit it, that all information contained herein is true, correct and complete, and that it is understood that all required items, statements, schedules, lists, and tables, are considered integral parts of this form. Person Signing the Report on Behalf of Reporting Manager: Name: Kenneth W. Stecher Title: Chief Financial Officer Phone: (513) 870-2000 Signature, Place and Date of Signing: /s/ Kenneth W. Stecher Fairfield, Ohio May 12, 2008 - ------------------------------------- -------------------- --------------- Report Type (Check only one.): [X] 13F HOLDINGS REPORT. (Check here if all holdings of this reporting manager are reported in this report.) [ ] 13F NOTICE. (Check here if no holdings reported are in this report, and all holdings are reported by other reporting manager(s).) [ ] 13F COMBINATION REPORT. (Check here if a portion of the holdings for this reporting manager are reported in this report and a portion are reported by other reporting manager(s).) List of other Managers Reporting for this Manager: N/A

FORM 13F SUMMARY PAGE Report Summary: Number of Other Included Managers 1 Form 13F Information Table Entry Total: 4 Form 13F Information Table Value Total 57,145 (thousands) List of Other Included Managers: No. File No. Name - --- -------- ---- 01 028-10798 Cincinnati Financial Corporation 2

COLUMN 2 COLUMN 3 COLUMN 4 COLUMN 5 COLUMN 6 COLUMN 7 COLUMN 8 -------- --------- --------- -------------- ------------ -------- ------------------------- TITLE OF SHARES/ SH/ INVESTMENT ISSUER CLASS CUSIP FMV (000) PRINCIPAL PRN DIS OTH MGRS SOLE SHARED NONE ------ -------- --------- --------- --------- --- ------------ -------- -------- --------- ---- FIFTH THIRD BANCORP COMMON 316773100 27,196 1,300,000 SH SHARED-OTHER 01 -- 1,300,000 -- JOHNSON & JOHNSON COMMON 478160104 9,731 150,000 SH SHARED-OTHER 01 -- 150,000 -- PROCTER & GAMBLE CORPORATION COMMON 742718109 10,511 150,000 SH SHARED-OTHER 01 -- 150,000 -- U S BANCORP COMMON 902973304 9,708 300,000 SH SHARED-OTHER 01 -- 300,000 -- 57,145 3

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