The aim of this paper is to investigate how children in primary school can apply two phonological rules, i.e. lateralization of nasals and nasalization of laterals, to the sequences of /l+n/ and /n+l/ generated by morpheme concatenation. To measure children's ability to apply the two rules, this paper carried out an experiment in which children read target words with the presence of these sequences contained in carrier sentences. The findings of the experiment are as follows. First, regarding /l+n/ sequences where the nasal is realized as [l] in standard pronunciation, the pattern of phonetic realization shows that the ratio the application of the lateralization rule to spelling pronunciation are almost equal among the fourth grade students. This result contrasts with the experiment on the identical sequences for adults in which 90% of subjects pronounced as [ll]. This implies that the fourth grade students do not adequately exploit the application of the lateralization rule. On the other hand, the application of the nasalization rule to /n+l/ sequences shows a better result in that only 20% of the fourth grade students read them as [nl]. The rest pronounces them as either [ll] or [nn]. This indicates that the fourth grade students can achieve the application of lateralization or nasalization rules in the same way. Second, the paper measures the frequency of the application of these phonological rules between the first and the fourth grade students. The result illustrates that the latter attains better scores than the former, which suggests that older students have more adequate ability to apply phonological rules to these two types of sequences. Finally, in terms of gender, there are no significant differences with respect to the ability of rule application to these sequences. The experiment conducted in this paper shows various aspects of phonological awareness in regard to how ill-formed consonant clusters are phonetically manifested. The result of the experiments can provide basic data for the test of reading ability and phonological processing. (Chungnam University)