Abstract： Objective To compare the efficacy of and adverse reactions to a fractional micro-plasma radio-frequency technology versus fractional ultrapulsed CO2 laser in the treatment of atrophic acne scars.Methods Twenty-one patients with atrophic acne scars were enrolled in this study.Half of each subject's face was treated with micro-plasma,and the other half with fractional ultrapulsed CO2 laser,for one session.Treatments were randomly administered in a split-face manner.The efficacy and adverse effects were evaluated 6 months after the treatment by using the following outcome parameters:ECCA grading scale (échelle d' évaluation clinique des cicatrices d'acné),degrees of post-treatment pain and edema,time taken for crusting and durations of inflammatory erythema,patients' subjective rating of improvement in scar by using a quartile grading scale.A non-parametric rank test was conducted to compare the efficacy and adverse effects between the two treatments.A scar model was established on both ears of a New Zealand big ear rabbit,and treated with the CO2 laser and micro-plasma respectively,immediately followed by the resection of scar tissue for the observation of histological changes.Results A decrease of ECCAscore was observed in 90.5％ (19/21) of the patients after micro-plasma treatment,and in 86.7％ (18/21) after CO2 laser treatment; no significant difference was observed in the response rate (P ＞ 0.05).In detail,ECCA score decreased by 31.5％ (from 50.71 to 34.76 ) after micro-plasma treatment,compared to 29.9％ (from 53.57 to 38.10) after CO2 laser treatmet.Mild edema was observed after micro-plasma treatment,with the duration of erythema and crusting being 13.95 days and 6.95 days,respectively,compared to 45.81 days and 10.10 days respectively,after CO2 laser treatment.Pigmentation occurred in none of the patients after micro-plasma treatment,but in 19％ after CO2 laser treatment.Animal experiment showed that microscopic ablation zones were broad and shallow after micro-plasma treatment,but narrow and deep after CO2 laser treatment.Conclusions Fractional micro-plasma and CO2 laser are both effective for the treatment of atrophic acne scars,but the former seems to have less side effects with a lower incidence of pigmentation.