This study examined how language knowledge and item properties (i.e., semantic relatedness and position) influenced Chinese missing logographeme effects. Eighty-four Chinese readers and 53 English readers were asked to search for the Chinese logographeme 口 while reading a Chinese prose passage. The target 口 appeared in five different positions (i.e., left, right, top, bottom, or inside), varying its degree of semantic relatedness to its embedded characters. The generalized linear mixed-effect model revealed a significant interaction between semantic relatedness and position in Chinese, but not in English, readers when visual complexity and frequency were controlled. For Chinese readers, a higher omission rate occurred when 口 appeared in the top and inside positions and exhibited low semantic relatedness with its embedded characters, whereas 口 was omitted more when it was positioned on the right and exhibited high semantic relatedness to its embedded characters. English readers exhibited a different omission pattern: 口 was omitted more when it appeared in the left or right position irrespective of semantic relatedness. In addition, 口 was omitted more in the inside, rather than the bottom, position. These findings suggest that the omission rate of the logographeme is determined by item properties at the sublexical level and the reader’s language knowledge.