The purpose of this study was to analyze the structure and elements of argument in pre-service biology teachers’ SSI related argument writing. For this purpose, twenty - two pre-service biology teachers wrote argument four times. We analyzed the structure and level of argument in the results of writing by pre-service biology teachers. In the result of the analysis, pre-service biology teachers suggested the claim and the basis in the first writing related to SSI. However, it was not enough to use the rebuttal, warrant and backing. As the demonstration theory and writing practice were repeated, there were few cases in which the claim and data were presented. Also, pre-service biology teachers utilized the elements of argument evenly. Especially, the average of the first writing was 2.86. And since then, the argument level average had steadily increased to 3.68, 4.36, and 4.70. This result showed that the argument theory class and the demonstration writing practice had a positive effect on the improvement of demonstrative writing ability of the pre-service biology teachers.