Thanks for your response. I realized that in my application, I have lot of events being triggered whenever each checkbox value is changed and the implementation of the event handlers need to be refactored for performance gain. this was helpful to resolve it. 

The methods did not help solve the issue. I'm trying to see how to create a sample of the issue or are there any other suggestions to the code below?? because I can't seems to identify how the property change notifications affects the performance but I see that the code { c.Value = CheckState.Checked} takes longer time to set the Value property {up to some secs per cell Value change) and browsing through the forum, I t was suggested to try to use InitializeRow() to change the values. I don't know how to do that.

Thanks

                BeginUpdate();
                SuspendRowSynchronization();

                try
                {


                    foreach (UltraGridCell c in Selected.Cells) // Selection were made with individual cell select
                    {
                        c.Value = CheckState.Checked;

                    }
                }
                finally {

                    ResumeRowSynchronization();

                    EndUpdate();
                }

Yes a select-all happens on the user side. The user can Shift+Click a collection of rows  at once and then hit the Space-key to check all boxes. So when the user makes the selection, ,y logic is to add all the selection to the collection "Selected" and then try to update the Cell.Value since I can not set Cell.Text {which i presume might be faster}