Zoom is a property of the Window-object. Assuming the application object is $ex.

$ex->Windows(1)->{Zoom} = 75;
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Code not tested but HTHA.

    #!/usr/bin/perl -w


    use strict;
    use Cwd;
    use Win32::OLE;
    use Win32::OLE::Const 'Microsoft Excel';


    my $application = Win32::OLE->new("Excel.Application");
    my $workbook    = $application->Workbooks->Add;
    my $worksheet   = $workbook->Worksheets(1);
    my $window      = $application->Windows(1);


    # Set the sheet zoom level.
    $window->{Zoom} = 75;


    # Write some text.
    $worksheet->Cells(1,1)->{Value} = "Hello World";


    my $dir = cwd();

    $workbook->SaveAs({FileName   => $dir . '/win32ole.xls'});
    $workbook->Close;


    __END__
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--
John.