This experimental study sought to investigate the effects of task-based language teaching (TBLT) when utilized in two learning environments, namely face-to-face (F2F) and blended learning (BL) and face-to-face on the speaking skills of Thai EFL undergrad learners. This study aimed to: 1) compare the learners’ improvement in speaking ability between the TBLT face-to-face group and the BL +TBLT group, 2) investigate the effects of feedback on the TBLT group and the BL + TBLT group, and 3) explore learners’ attitudes towards the TBLT approach in the blended learning speaking course of the experimental group. The participants were separated into two groups by using a purposive sampling method. In the experimental group, the participants needed to study speaking through task-based learning in blended learning class. There were 44 participants in the experimental group from Thai major. In the control group, there were 44 participants in the control group from business administration major. This group studied speaking through task-based learning in class. Three research instruments were used to collect data: pre-post-tests, the teacher’s observation, and semi-structured interviews. Mean (x̄), Standard Deviation (S.D.), and descriptive analysis were used in this study in order to describe the statistics. The results showed that: 1)the findings indicate that the participants showed an increase in speaking proficiency in all areas: accuracy, fluency, interactive communication, task completion, pronunciation and vocabulary. 2) demonstrated that the speaking problems of both the control and experimental groups decreased; moreover, the overall mean speaking scores of the control and the experimental group both tended to increase. 3)presented that the learners in the experimental group demonstrated a positive attitude towards the combination of task-based learning and blended learning. In addition, the TBLT that was implemented in both groups played a major role in encouraging the participants to complete the speaking tasks.