L2 learners tend to encounter and use morphological derivatives more frequently as their L2 skills develop. To pronounce the morphological derivatives correctly, L2 learners have to be aware of the phonological changes occurring in the derivatives with affixation. The four phonological rules (stress shift, vowel laxing, consonant coalescence, and vowel reduction) in English, applying to morphological derivatives, are examined with respect to the entities that the rules affect (stress, vowels, and consonants); the number of rules (only one and more than one rule); and rule interaction (interacting and non-interacting) in L2 phonological acquisition. This study reveals that 1) the accuracy of consonant coalescence is highest although its significance with respect to the accuracy of stress shift and vowel laxing varies according to the number of rules; 2) stress shift and vowel laxing show different order in accuracy depending on the number of rules; 3) the three rules (stress shift, vowel laxing, and consonant coalescence) exhibit distinct behaviors with respect to the number of rules; 4) in the interacting rules, the accuracy of the fed rule (vowel reduction) is significantly lower than the feeding rule (stress shift) while in the non-interacting rules, the accuracy of one rule appears to have no influence on that of the other rule. Based on the results, implications for teaching pronunciation of the derivatives are suggested.