A manufacturing method of a semiconductor memory device includes the following steps. A semiconductor substrate is provided. A memory cell region and a peripheral region are defined on the semiconductor substrate. A dielectric layer is formed on the semiconductor substrate. A first trench penetrating the dielectric layer is formed on the memory cell region, and a second trench penetrating the dielectric layer is formed on the peripheral region. A metal conductive layer is formed. The first trench and the second trench are filled with the metal conductive layer for forming a bit line metal structure in the first trench and a first metal gate structure in the second trench. In the present invention, the replacement metal gate process is used to form the bit line metal structure for reducing the electrical resistance of the bit lines.