Ferroelectric/antiferroelectric thin/thick films with large positive or negative electrocaloric (EC) effects could be very useful in designing commercial refrigeration devices. Here, a giant negative EC effect (maximum Δ T ∼ −42.5 K with Δ S ∼ −29.3 J K −1 kg −1 ) comparable to the best positive EC effects reported so far is demonstrated for 0.5(Ba 0.8 Ca 0.2 )TiO 3 -0.5Bi(Mg 0.5 Ti 0.5 )O 3 (BCT-BMT) lead-free relaxor ferroelectric thin films prepared on Pt(111)/TiO x /SiO 2 /Si substrates using a sol-gel method. An electric-field induced structural phase transition (nanoscale tetragonal and orthorhombic to rhombohedral) along the out-of-plane 111 direction plays a very key role in developing the giant negative EC effect. This breakthrough will pave the way for practical applications of next-generation refrigeration devices with high cooling efficiency in one cycle by ingeniously utilizing and combining both the giant negative and positive EC effects. Moreover, a large energy density of 51.7 J cm −3 with a high power density of 1.15 × 10 10 W kg −1 at room temperature is also achieved in the thin film, indicating that it is also an attractive multifunctional material for energy storage. Ferroelectric/antiferroelectric thin/thick films with large positive or negative electrocaloric (EC) effects could be very useful in designing commercial refrigeration devices.