Herein, we report an electrochemical multicomponent one-pot cascade protocol for the synthesis of 4-selenylsulfonylpyrazoles from sulfonohydrazides, pentane-2,4-diones and diselenides under catalyst-, chemical oxidant- and electrolyte-free conditions. This method features good functional group tolerance, step economy, mild reaction conditions, environmental friendliness, easy operation with cheap reagents, scaled-up synthesis and high yields, providing a promising strategy to construct pyrazole derivatives containing selenium and sulfonyl, which is widely used in drugs, agricultural chemicals and biologically active compounds. Notably, the representative compound 1-((4-fluorophenyl)sulfonyl)-3,5-dimethyl-4-(phenylselanyl)-1 H-pyrazole 4jaa can inhibit the proliferation of human triple-negative breast cancer cells with an IC ₅₀ value of 5.35 ± 0.76 μM. Moreover, the proposed mechanism is supported by control experiments and density functional theory calculations.