<PAGE>
SUPPLEMENT DATED SEPTEMBER 27, 1996 TO THE PROSPECTUS DATED FEBRUARY 1, 1996
ADVANTUS Mortgage Securities Fund, Inc.
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400 Robert Street North - St. Paul, Minnesota 55101 - 1-800-443-3677
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The "Annual Fund Operating Expenses" table and the "Shareholder Expense
Example" on pages 6 and 7, respectively, of the Prospectus have been amended to
read as follows:
<TABLE>
<S> <C> <C> <C>
ANNUAL FUND OPERATING EXPENSES
(AS A PERCENTAGE OF AVERAGE
NET ASSETS)
INVESTMENT ADVISORY FEES .575% .575% .575%
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RULE 12b-1 FEES (AFTER EXPENSES WAIVED) * .25%** 1.00% 1.00%
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OTHER EXPENSES (AFTER EXPENSES WAIVED)*** .125% .125% .125%
------ ----- -----
TOTAL FUND OPERATING EXPENSES
(AFTER EXPENSES WAIVED)*** .95% 1.70% 1.70%
------ ----- -----
</TABLE>
<TABLE>
<S> <C>
*A LONG-TERM SHAREHOLDER MAY PAY MORE IN ASSET-BASED DURING THE CURRENT FISCAL YEAR, BUT IT RESERVES THE RIGHT TO
SALES CHARGES THAN THE ECONOMIC EQUIVALENT OF THE MAXIMUM CEASE SUCH WAIVER, IN WHOLE OR IN PART, AT ANY TIME.
FRONT-END SALES CHARGE PERMITTED BY THE NATIONAL ASSOCIATION ***THE FUND'S INVESTMENT ADVISER AND MIMLIC SALES
OF SECURITIES DEALERS, INC. (SEE "MANAGEMENT OF THE VOLUNTARILY ABSORBED OR WAIVED CERTAIN EXPENSES OF THE FUND
FUND--THE UNDERWRITER AND PLANS OF DISTRIBUTION"). FOR THE YEAR ENDED SEPTEMBER 30, 1995. IF THE FUND HAD BEEN
**THE FUND HAS ADOPTED A PLAN OF DISTRIBUTION, PURSUANT CHARGED FOR THESE EXPENSES, THE RATIO OF TOTAL FUND
TO RULE 12B-1 UNDER THE INVESTMENT COMPANY ACT OF 1940, OPERATING EXPENSES TO AVERAGE DAILY NET ASSETS WOULD HAVE
WHICH PROVIDES FOR THE PAYMENT TO MIMLIC SALES OF A BEEN 1.42% FOR CLASS A SHARES, 2.11% FOR CLASS B SHARES AND
DISTRIBUTION FEE EQUAL TO AN ANNUAL RATE OF .30% OF AVERAGE 2.11% FOR CLASS C SHARES. IN ADDITION, IT IS THE FUND'S
DAILY NET ASSETS ATTRIBUTABLE TO CLASS A SHARES OF THE FUND. INVESTMENT ADVISER'S PRESENT INTENTION TO ABSORB OTHER
MIMLIC SALES IS CURRENTLY WAIVING THAT PORTION OF EXPENSES DURING THE CURRENT FISCAL YEAR WHICH EXCEED, AS A
DISTRIBUTION FEE WHICH EXCEEDS, AS A PERCENTAGE OF AVERAGE PERCENTAGE OF AVERAGE DAILY NET ASSETS, .125%. THE FUND'S
DAILY NET ASSETS ATTRIBUTABLE TO CLASS A SHARES, .25%. IT IS INVESTMENT ADVISER ALSO RESERVES THE OPTION TO REDUCE THE
MIMLIC SALES' PRESENT INTENTION TO WAIVE DISTRIBUTION FEES LEVEL OF OTHER EXPENSES WHICH IT WILL VOLUNTARILY ABSORB.
AS SUCH LEVEL
</TABLE>
F.50343 9-96
<PAGE>
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SHAREHOLDER EXPENSE
EXAMPLE You would pay the following expenses on a $1,000 investment assuming
(1) 5% annual return and (2) redemption at the end of each time period.
YEAR REDEEMED CLASS A CLASS B CLASS C
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1 $ 59 $ 67 $ 17
3 79 89 54
5 100 107 92
10 161 172* 181*
An investor would pay the following expenses on the same investment in Class B
shares, assuming no redemption:
YEAR REDEEMED CLASS B
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1 $ 17
3 54
5 92
10 172*
*REFLECTS CONVERSION OF CLASS B SHARES TO CLASS A SHARES (WHICH PAY LOWER
ONGOING EXPENSES) APPROXIMATELY SEVEN YEARS AFTER PURCHASE.
**REFLECTS CONVERSION OF CLASS C SHARES TO CLASS A SHARES (WHICH PAY LOWER
ONGOING EXPENSES) APPROXIMATELY EIGHT YEARS AFTER PURCHASE.
THE EXAMPLES CONTAINED IN THE TABLE SHOULD NOT BE CONSIDERED A REPRESENTATION
OF PAST OR FUTURE EXPENSES. ACTUAL EXPENSES MAY BE GREATER OR LESS THAN THOSE
SHOWN.
