In order to clarify what causes the difference in the electronic properties between K-salt and NH4-salt, we systematically studied the effects of uniaxial strain on alpha-(BEDT-ITF)(2)MHg(SCN)(4) [M=K, NH4]. Resistance measurements were performed under the uniaxial strain applied along the a-, b*- and c-axes independently. Superconductivity like NH4-salt was induced in the K-salt under the the c-axis uniaxial strain, while the density wave state like K-salt was induced in NH4-salt under the a-axis uniaxial strain. It was found that the ratio of the inplane lattice constant c/a plays a key role in dominating their electronic properties.