Augmentative and alternative communication (AAC) systems are not well-known and broadly used in Thailand. To begin introducing AAC systems and interventions to children with complex communication needs in Thailand, understanding speech-language pathologists' (SLPs) perceptions toward various AAC systems is an important first step. This study assessed SLPs' perceptions of three AAC modalities: gestural communication, communication boards, and iPad-based speech-output technologies. A total of 78 SLPs watched three video vignettes of a child using each mode and rated their impressions of intelligibility, ease of learnability and use, effectiveness, and preference. Then they were asked to rate factors on visual analog scales that provided additional insights into their rationales and their preferences for AAC modalities for nonverbal clients and for themselves if they were nonverbal. The results indicated that most of the SLPs rated iPad-based speech-output technologies as being the more intelligible, effective, and preferred mode of communication. Gestural communication was rated as the easiest mode to learn and use for a child with complex communication needs. Despite infrequent use of iPad-based speech-output technologies in Thailand, SLPs' ratings indicated high social acceptance of this modality for promoting communication abilities of children with complex communication needs. Results also revealed some biases and lack of knowledge about AAC systems in Thailand.