Disable the jquery multiselect

$("#mymultiselect").multiselect("disable");

should do the trick.

HTML:

<select id="test001" multiple="multiple" size="5"> 
    <option value="option1">Option 1</option> 
    <option value="option2">Option 2</option> 
    <option value="option3">Option 3</option> 
    <option value="option4">Option 4</option> 
    <option value="option5">Option 5</option> 
</select> 

Javascript:

$("#test001").multiselect({
    minWidth: 300,
    height: 150,
    header: false,
    noneSelectedText: "Select",
    selectedList: 3
});

Calling $("#test001").multiselect("disable"); will disabled the multiselect.

Here's an jsfiddle

if you change find("input:checked").length > 3 you can possible to select 3 value For ur wish you can change the.. value and get... your answer

  if( $(this).multiselect("widget").find("input:checked").length > 2 ){

I've updated the original fiddle posted earlier adding an enable button as well for quicker reference. http://jsfiddle.net/cSq2L/180/

$("#test001").multiselect({
        minWidth: 300,
        height: 150,
        header: false,
        noneSelectedText: "Select",
        selectedList: 3
    });


$("#changeStatus").click(function()
   {
   $("#test001").multiselect("disable");
   });                   

   $("#changeStatuss").click(function()
   {
   $("#test001").multiselect("enable");
   });     

Don't know how much JavaScript you know, but $widget.multiselect('disable'); will disable the selector (stored in the variable $widget). And by replacing disable with enable you can enable it.

So just run the function with the correct disable/enable setting and you can do it based on any condition.

Terw