This study investigates the growing interest in ChatGPT's role in education, with a particular focus on its effects on postgraduate students' English-speaking proficiency--an area predominantly explored through theoretical perspectives with limited empirical evidence. The research aims to address this gap by examining the experiences and perceptions of Chinese postgraduate students using ChatGPT for IELTS speaking practice. Adopting a mixed-methods approach, the study integrates experimental engagement with ChatGPT, analysis of reflective diaries, and responses from questionnaires to evaluate the platform's efficacy in enhancing enthusiasm for English language practice. The findings reveal a positive impact of ChatGPT on learners' engagement, demonstrated by an increase in practice frequency. A significant correlation was observed between regular interaction with ChatGPT and improvements in English grammar skills among participants. Thematic analysis of reflective diaries underscored ChatGPT's contribution to language learning and students' proactive approach to acquiring English-speaking skills. However, there was a consensus among students regarding the need for more human-like interactions from ChatGPT. This study provides valuable insights into the potential of chatbots to enhance English-speaking skills in EFL contexts, offering practical recommendations for educators and developers to optimize chatbot learning experiences.