This work presents a new idea to fabricate an enzyme glucose sensor. A bio-composite was assembled by in situ reducing Ag⁺ to Ag in glucose oxidase (GOD) solution. In this way, metallic silver can directly deposit onto the GOD surface and induce tight contact between Ag and GOD. The obtained composites were characterized by FESEM, EDS mapping, FTIR, CD, and electrochemical measurements. The Ag–GOD composite formed by an in situ reducing process exhibits facile, direct electrochemistry and good electrocatalytic performance without any electron mediator. The designed glucose biosensor shows high sensitivity, high selectivity, long life and accurate measurement in real serum samples, which is contributed to by a fast, direct electron transfer due to close proximity between Ag and GOD.