Chirality plays an important role in chemistry, biology, and materials science. The recent discovery of the B40-/0 borospherenes marks the onset of a class of boron-based nanostructures. Here we report the observation of axially chiral borospherene in the B39- nanocluster on the bases of photoelectron spectroscopy, global minimum searches, and electronic structure calculations. Extensive structural searches in combination with density functional and CCSD(T) calculations show that B39- has a C3 cage global minimum with a close-lying C2 cage isomer. Both the C3 and C2 B39- cages are chiral with degenerate enantiomers. The C3 global minimum consists of three hexagons and three heptagons around the vertical C3 axis. The C2 isomer is built on two hexagons on the top and at the bottom of the cage with four heptagons around the waist. Both the C3 and C2 axially chiral isomers of B39- are present in the experiment and contribute to the observed photoelectron spectrum. The chiral borospherenes also exhibit three-dimensional aromaticity, featuring sigma and pi double delocalization for all valence electrons. Molecular dynamics simulations reveal that these chiral B39- cages are structurally fluxional above room temperature, compared to the highly robust D2d B40 borospherene. The current findings add chiral members to the borospherene family and indicate the structural diversity of boron-based nanomaterials.