<p>Background: Laughter has been previously used to improve mental health and well-being in clinical and non-clinical populations. Tested laughter interventions have, however, incorporated a combination of methods, including laughter paired with deep breathing, stretching, musical activities, and/or meditation, making it challenging to establish the precise effect of laughter on well-being. Moreover, no published studies have explored online exposure to audio-visual human contagious laughter in relation to subjective well-being. Methods: A pilot study was conducted to determine the effectiveness of a five-day, online, audio-visual contagious laughter intervention on well-being in 100 adults. The WHO5 Wellbeing Index was administered pre-and post-intervention. Self-reported mood status was also ascertained using the EmojiGrid scale before and after each of the five audio-visual contagious laughter videos for those randomized to the experimental condition. Participants were also asked if they laughed along with the video after each day of viewing. Results: The adjusted mean difference in well-being score in the experimental group was 8.3 (95% CI: 0.7 to 15.8), p = 0.032. Self-rated mood status improved significantly for each day of the intervention (all p &lt; 0.001), although the mean changes in mood were noticeably modest. Conclusions: Findings from the study need to be replicated in other populations to either confirm or refute our results. Incorporating laughter as a regular lifestyle habit is free, and may enhance subjective well-being, should larger studies confirm our findings. Additional studies could be later conducted in clinical populations to determine the effectiveness of similar human, contagious laughter interventions. Our pilot randomized controlled trial to www.clinicaltrials.gov on 14 August 2025 NCT07123571.</p>