ABSTRACTThe results of this research are that law enforcement efforts by the Pontianak City Police Traffic Unit regarding engine replacement modifications on two-wheeled vehicles that do not carry out type test obligations are carried out through 2 (two) steps, namely, preventive efforts and repressive efforts. Preventive efforts are carried out by providing outreach as well as complaints and consultation services for people who are still confused about modifying motorized vehicles in accordance with applicable regulations. The repressive efforts were carried out in collaboration with the West Kalimantan Provincial Transportation Service carrying out a joint operation (Operation Tata Order). The main obstacles faced by the Pontianak City Police are the lack of public participation and awareness of the law and the lack of special attention from police law enforcers.Keywords: Law Enforcement, Police, Modification, Engine Replacement. ABSTRAKHasil dari penelitian ini adalah bahwa upaya penegakan hukum oleh Satlantas Polresta Kota Pontianak terhadap modifikasi pergantian mesin pada kendaraan roda dua yang tidak melakukan kewajiban uji tipe dilakukan melalui 2 (dua) langkah yaitu, upaya preventif dan upaya represif. Upaya preventif dilakukan dengan memberikan sosialisasi serta layanan aduan dan konsultasi bagi masyarakat yang masih kebingungan dalam hal modifikasi kendaraan bermotor sesuai dengan peraturan yang berlaku. Adapun upaya represif dilakukan dengan bekerja sama dengan Dinas Perhubungan Provinsi Kalimantan Barat melakukan operasi gabungan (Operasi Tata Tertib). Hambatan utama yang dihadapi Polresta Kota Pontianak yaitu kurangnya partisipasi dan kesadaran masyarakat terhadap hukum serta kurangnya perhatian khusus dari penegak hukum kepolisian Kata Kunci: Penegakan Hukum, Polresta, Modifikasi, Pergantian Mesin.