A cross sectional research was undertaken with sixty university students to know whether levels of proficiency interact with the realization of English dative case in Iranian EFL learners’ performance and whether Iranian EFL learners aware of discourse constraint in English dative case. The research shows that Iranian learners learn dative non-alternation first, because dative non-alternation structures are somehow compatible with Persian structures. But, in the case of dative alternation Iranian learners encounter with some problems. So the usage of this English structure depends on the proficiency levels of the learners; the higher of the proficiency level, the more usage of dative alternation. The subjects were aware of discourse constraint in one sentence, but they were not aware of this constraint in the other sentence. It seems that they are not aware of the existence of this constraint; they just intend to use [NP PP] complement. Keywords: dative alternation, dative non-alternation, discourse constraint, proficiency level Iranian learners’ performanc
