Using content analysis, this study examined the effects of several messaging strategies in YouTube videos promoting human papillomavirus vaccines in Korea. It analyzed a total of 201 videos, focusing on five message strategies-temporal framing, narrative format, gain-loss framing, emotional appeals, and message sensation value. The analysis revealed that the creators of these YouTube videos frequently utilized all of these strategies, except for emotional appeals. It also showed that present-focused framing was effective in eliciting positive responses from viewers, and not including gain-loss framing was more effective in provoking responses. Meanwhile, message sensation values were found to increase both positive and negative viewer responses.