Compositions including a recombinant respiratory syncitial virus (RSV) Fusion (F) polypeptide that is stabilized in the pre-fusion conformation are described. The RSV F polypeptide includes at least one mutation as compared to a wild type RSV F polypeptide and the at least one mutation is a) a mutation of the amino acid aspartic acid (D) on position 486, b) a mutation of the amino acid aspartic acid (D) on position 489, or c) a mutation of the amino acid serine (S) on position 398 and/or the amino acid lysine (K) on position 394. Compositions including an isolated nucleic acid molecule encoding the stable RSV F polypeptides are also described.