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Abstract We study the exotic decay of the 125 GeV Higgs boson (h) into a pair of light spin-0 particles ( $$\phi $$ ϕ ) which subsequently decay and result in a 4b final state. This channel is well motivated in models with an extended Higgs sector. Instead of searching at the Large Hadron Collider (LHC) and the high luminosity LHC (HL-LHC) which are beset by large standard model (SM) backgrounds, we investigate this decay channel at the much cleaner Large Hadron Electron Collider (LHeC). With some simple selection cuts this channel becomes nearly free of background at this ep machine, in sharp contrast to the situation at the (HL-)LHC. With a parton level analysis we show that for the $$\phi $$ ϕ mass range $$[20,60]~{\text{ GeV }}$$ [ 20 , 60 ] GeV , with $$100~{\text{ fb }^{-1}}$$ 100 fb - 1 luminosity the LHeC is generally capable of constraining $$C_{4b}^2\equiv \kappa _{V}^2\times {\mathrm {Br}}(h\rightarrow \phi \phi )\times {\mathrm {Br}}^2(\phi \rightarrow b\bar{b})$$ C 4 b 2 ≡ κ V 2 × Br ( h → ϕ ϕ ) × Br 2 ( ϕ → b b ¯ ) ( $$\kappa _{V}$$ κ V denotes the $$hVV(V=W,Z)$$ h V V ( V = W , Z ) coupling strength relative to the SM value) to a few percent level ( $$95\%$$ 95 % CLs). With $$1~{\text{ ab }^{-1}}$$ 1 ab - 1 luminosity $$C_{4b}^2$$ C 4 b 2 at a few per mille level can be probed. These sensitivities are much better than the HL-LHC performance and demonstrate the important role expected to be played by the LHeC in probing exotic Higgs decay processes, in addition to the already proposed invisible Higgs decay channel.