Equiatomic CrMnFeCoNi high entropy alloy (HEA) was firstly used as sintering aid for preparation of B4C ceramics by spark plasma sintering (SPS) at temperature ranging from 1500 to 2100 degrees C. The mechanical properties of B4C-5 vol.% HEA ceramics as well as densification mechanisms during the SPS process were investigated. B4C-5 vol.% HEA ceramic sintered at an optimized low temperature of 1950 degrees C obtained an attractive combination of properties, including a relative density of 99.27%, a microhardness of 3427 Hv(0.2) and a rupture strength of 619 MPa, which was 37% higher than the highest strength of pure B4C ceramic. The densification mechanism during the SPS was elucidated by the stress exponent n and the apparent activation energy Q(d). At low effective compaction stresses (n = 1, Q(d) = 519.5 +/- 82.6 kJ/mol) in the temperature range of 1700-1950 degrees C, the densification was controlled by grain-boundary sliding. At high effective compaction stresses (n around 2.5 and 5.5), the densification mechanism is transformed to dislocation climb, which was verified by transmission electron microscopy. (C) 2018 Published by Elsevier B.V.