In second language acquisition, learners often replace foreign and unfamiliar sounds in the second language with the ones available in their first language. These replacements are obviously not random; however, what determines how learners replace foreign sounds? The present study is interested to find out the rules governing these replacements, particularly by analyzing common replacements in five target languages and by comparing the articulatory features between the original foreign sounds and the replacing sounds; and see if the occurrence frequency of the phonemes available in the first language would affect the results of these replacements.