Abstract: Background and Objective: The German cockroach (Blattella germanica) is a well-known urban insect pest that has become resistant to synthetic insecticides. Hence, the alternative potent insecticides, synthesized from natural substances such as lemongrass essential oil are urgently needed. Its main objective was to experimentally test the efficacy and residual activity of lemongrass essential oil (Cymbopogon flexuosus) against German cockroache’s population. Materials and Methods: This study was conducted at the Research Laboratory of Animal Physiology, Department of Biology, Andalas University, Indonesia. It used lemongrass essential oil with different concentrations through Contact Toxicity Test (3.15 mg cm–2), Fumigation Toxicity Test (1 g cm–3) and Repellency Test (0.16 mg cm–2). Results: Lemongrass essential oil was effective in killing German cockroaches through Contact Toxicity Test (LT90<24 h), lemongrass essential oil at sub-lethal concentration behaved as repellent to German cockroaches with 100% repellency values, observed effectively for 48 h of trial. Conclusion: Lemongrass essential oil is potential to be an alternative insecticide in controlling the resistance of German cockroaches through contact and repellency applications.