The present study investigated the production of English passive constructions among Thai learners as syntactic asymmetry of the construction in question in Thai and English can be attested. In this study, English verbs were categorized into two types: Verb Type 1 and Verb Type 2. The former refers to those that can naturally occur in Thai "thùuk" passives while the latter includes those that sound unnatural when used with the same marker. Forty undergraduate students, including 20 advanced and 20 intermediate learners, were asked to complete sentences, each of which consisted of at least three given words: one noun placed as the subject, one verb, and another noun. Results showed that it can be assumed that language transfer is a factor leading to high and low numbers of passivization with Verb Type 1 (positive transfer) and Verb Type 2 (negative transfer), respectively, regardless of their groups. Learners' proficiency levels play a vital role in the number of passive sentences produced in both verb types, showing statistical significance (p < 0.05). The differences between the verb types, conversely, are not statistically significant across the two groups