Mom died with no will. Im the only heir /child. She had no other children

If the check is made out to the estate, you must open an estate.  Whether you need a full probate with a court hearing or can use a Small Estate Affidavit depends on what she left and where.  Please contact a local probate lawyer to discuss what route is available to you and whether the cost of probating the estate would exceed the amount in the check.  In some cases it is better to let the check go to unclaimed property and go through the hassle of trying to claim the proceeds years from now.