Sage Stallone's mother has asked a judge to let her administer her son's estate ... which she values at $40,000.
Sasha Madron claims Sage died without a will, and left personal property valued at 40 grand.
Sasha wants full authority to make decisions on behalf of the Estate.
Sage died in July. The coroner says Sage died as a result of a heart attack, not drug use -- in fact, no drugs were found in his system at the time of his death.