A forming die assembly for microcomponents includes a forming die, a plunger, and a punch. The forming die is formed with an outer die, an inner die, a storage portion formed at the inner die, and a punch hole formed at the inner die. The inner die slidably inserted into the outer die forms a part of a cavity between the inner die and the outer die. The storage portion stores a raw material with a metal powder and a binder having plasticity. The punch hole connects the cavity and the storage portion and forms a gate therebetween. The plunger slidably inserted into the storage portion fills the raw material stored in the storage portion into the cavity through the punch hole. The punch is slidably inserted into the plunger, and it closes the gate and compresses the raw material in the cavity.