Assembly.load and [Serializable] not work

In Game.dll
[Serializable]
public class ABC
{
public int a = 1;
}

ABCBehaviour : MonoBehaviour
{
public ABC data = new ABC();
}

when In My Unity Project I call Assembly.load("Game.dll"),then Load the asset which attached ABCBehaviour.
However,When the asset Loaded Class ABC is null.
Who can help me,Thanks!