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The purpose of this article is to determine the levels of understanding for solving Stoichiometry problems from the aspect of macroscopic, microscopic and symbolic representations of high, average and low achieving students after infusion of metacognitive skills. Nine form four students aged sixteen years old from a secondary school in Kuala Lumpur, Malaysia were involved in this research. Data were collected through thinking aloud sessions and documents of students’ worksheets. Findings showed that the level of understanding from the aspect of the macroscopic, microscopic and symbolic representations among high achieving students appeared high and solved all the Stoichiometry problems related to balancing chemical equations at the end of the infusion. The average and low achieving students also seemed to understand the three levels of representations and could solve most of the problems except that they could not understand the mole ratio in balancing chemical equations. This implies that the understanding of the mole ratio is necessary for solving stoichiometric problems.