Hilkka Rantaseppä-Helenius (1925 – 1975) was a Finnish astronomer.
Rantaseppä-Helenius began studying mathematics in hopes of becoming a teacher. Finnish astronomer Yrjö Väisälä inspired her to become an astronomer instead.
Rantaseppä-Helenius worked on observing minor planets. She worked as an assistant at Tuorla Observatory from 1956 to 1962. In 1962 she became an observer when a vacancy became available. She remained an observer until 1975. She was also involved in building the Kevola Observatory by Tähtitieteellis-optillinen seura (Astronomy-Optical Society) on her own property in 1963.
Rantaseppä-Helenius died at age 50 in an accident. The asteroid 1530 Rantaseppä is named after her.