Some users may want to remove the Company field requirement on Leads. This is only possible if Person Accounts have been enabled for the Org.
If Person Accounts have been activated, the Company field requirement can be modified. To change this requirement, edit the Lead Page Layout, double click on the Company field, then deselect the Required check box (step by step given below):
1) Go to Setup | Customize | Leads | Page Layouts
2) Click Edit next to the Page Layout name
3) Click on the wrench icon for the Company field
4) Deselect the Required checkbox and click OK
5) Save the Layout
When converted, a Lead without a Company will create a Person Account; the Name field of the Lead will be mapped to the Person Account's Name field.
Person Accounts may only be enabled for Enterprise Edition, Unlimited Edition, and Developer Edition.
It is not possible to remove the Lead Company field requirement for Professional Edition or Group Edition.