Water splitting into hydrogen and oxygen in order to store light or electric energy requires efficient electrocatalysts for practical application. Cost‐effectiveness, abundance, and efficiency are the major challenges of the electrocatalysts. Herein, this paper reports the use of low‐cost 304‐type stainless steel mesh as suitable electrocatalysts for splitting of water. The commercial and self‐support stainless steel mesh is subjected to exfoliation and heteroatom doping processes. The modified stainless steel electrocatalyst displays higher oxygen evolution reaction property than the commercial IrO2, and comparable hydrogen evolution reaction property with that of Pt. More importantly, an all‐stainless‐steel‐based alkaline electrolyzer (denoted as NESSP//NESS) is designed for the first time, which possesses outstanding stability along with lower overall voltage than the conventional Pt//IrO2 electrolyzer at increasing current densities. The remarkable electrocatalytic properties of the stainless steel electrode can be attributed to the unique exfoliated‐surface morphology, heteroatom doping, and synergistic effect from the uniform distribution of the interconnected elemental compositions. This work creates prospects to the utilization of low‐cost, highly active, and ultradurable electrocatalysts for electrochemical energy conversion. Surface engineering of cost‐effective commercial stainless‐steel mesh is employed as 3D self‐supportive electrocatalysts for electrochemical water splitting. Benefiting from the highly active exfoliated surfaces and heteroatoms‐doping, the surface‐engineered stainless‐steel mesh displays outstanding oxygen evolution reaction, hydrogen evolution reaction, and overall water‐splitting performance, coupled with excellent ultralong stability.