Abstract: With the method of comparative physiology, tomato plants (Lycopersicon esculentum Mill), chlorella (Chlorella pyrenoidosa Chick), callus tissue (Parthenocissus tricuspidata Pench), and black Aspergilli (Aspergillus niger von Tieghem A.S. 3.316 and Aspergillus usamii Sakaguchi A.S. 3.758) were used as experimental materials to study their zinc requirements in relation to light. The results showed that the requirement of zinc of tomato plants was increased with the increase of light intensity. The growth of chlorella in light under mixotrophic condition required more zinc than those grown in the dark under heterotrophic condition. The growth of callus tissues required slightly more zinc under light than in the dark. However, the requirement of zinc in black Aspergilli was not affected by light or darkness. Therefore the physiological role of zinc in autotrophic plants can be considered as related to light and that in heterotrophic plants is not. On the other words, two kinds of physiological functions of zinc in plants could exist, one is related to light and the other is not. The former might be in connection with photosynthesis and the later might be related to the constitution of enzyme or to the synthesis of auxin.