Status epilepticus (SE) is a life-threatening medical and neurological emergency. Prompt recognition and treatment are essential to stop the seizure and improve patient outcomes. To elucidate which benzodiazepine should be used as the first-line treatment, a systemic search of the PubMed, Cochrane Central Register of Controlled Trials, and Igaku Chuo Zasshi databases was carried out to identify randomized controlled trials (RCTs) comparing i.v. administration of lorazepam and diazepam used for adult SE. The certainty of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation approach. Only two RCTs were finally analyzed among 2182 papers extracted. The SE definitions, inclusion criteria, and doses of the drugs differed in the two studies. Of 204 patients included, 103 and 101 patients were allocated to the lorazepam and diazepam groups, respectively. The pooled risk ratio (RR) and confidence interval (CI) for lorazepam treatment on seizure cessation (two RCTs, n = 204) showed a significantly superior effect of lorazepam over diazepam (RR, 1.24; 95% CI, 1.03-1.49). No statistically significant relationship was found for mortality (two RCTs, n = 204) (RR 0.43; 95% CI, 0.43-6.90), poor neurological outcome (one RCT, n = 134) (RR, 1.10; 95% CI, 0.59-2.04), hypotension (one RCT, n = 70) (RR, 2.68; 95% CI, 0.11-63.61), and respiratory depression (two RCTs, n = 204) (RR, 1.07; 95% CI, 0.48-2.48). The certainty of the evidence was rated as very low. The results of this meta-analysis of RCTs showed that i.v. lorazepam was better than i.v. diazepam for the cessation of adult SE.