Over the past decades, research on positive psychology for building strengths has proliferated. The present study aimed to explore the effect of gratitude in a 5-week positive psychology group program for undergraduate engineering students which included an intermediary 2-week gratitude intervention. In a mixed-design, 69 students from three engineering departments of the School of Pedagogical and Technological Education (ASPETE), assigned to the intervention (N = 34) and the control group (N = 35), with an average age of 21.52 years (SD= 4.63), were administered the Gratitude Questionnaire—six item form (GQ-6), the Modified Differential Emotions Scale (mDES), the Connor–Davidson Resilience Scale (CD-RISC), the Subjective Happiness Scale (SHS), and the Life Orientation Test—Revised (LOT-R). The condition experimental vs. control group was designated as the between-subjects factor, and time, that is, baseline vs. post intervention, was set as the within-subjects factor. Students who received the intervention reported significantly higher levels of gratitude. The increase in gratitude was due to the positive psychology group program. In addition, gratitude showed a significant effect on happiness and optimism, but failed to attain a significant impact on positive and negative emotions and resilience. Further research is needed to elucidate the effectiveness of positive psychology programs for undergraduate engineering students and the intervening cognitive processes.