Chaka Khan just won temporary custody of her 10-year-old granddaughter because the child's parents are drug addicts -- this according to legal docs obtained by TMZ.
Chaka filed a petition for appointment of guardianship last week -- claiming she has already "assumed on a day-to-day basis the role of the child's parent fulfilling both the child's physical and psychological needs for care and affection."
Chaka claims the child's mother -- who lives in the same house -- is incapable of caring for the girl because of a "heavy involvement in drugs."
Chaka's sister Tammy McCrary -- who was also awarded custody -- filed an additional statement in the petition, claiming Chaka's son "also uses and abuses drugs and other illegal substances."
The judge temporarily granted the petition for custody on September 6th ... and extended it today. A hearing is set for October to make it permanent.