Onibaba's literal meaning is Demon Hag.
The demon mask used in the movie inspired William Friedkin to use a similar design for the makeup in subliminal shots of a white-faced demon in The Exorcist (1973).
Initially refused a certificate in England by the BBFC in 1965, but resubmitted in 1968 where it was approved with an X classification albeit with some cuts.
The tall grass seen throughout the film is miscanthus or Japanese silver grass, in Japan it is known as susuki.
Historically, the events of Onibaba take place a brief time after the Battle of Minatogawa. This battle sparked a 50 year civil war known as the Nanboku-cho period, and lasted from 1336 to 1392. In the film, the character Hachi speaks of an attack by General Takauji Ashikaga, historically, Ashikaga would come to power in the 1330s.