Industri semen berperan penting dalam pembangunan infrastruktur dan ekonomi Indonesia. Untuk memperluas pengaruh di Asia Tenggara, Indonesia menerapkan strategi diplomasi ekonomi, salah satunya melalui akuisisi Thang Long Cement di Vietnam oleh Semen Indonesia Group (SIG). Langkah ini memperkuat posisi Indonesia di industri semen regional sekaligus meningkatkan daya saing internasional. Penelitian ini menganalisis peran diplomasi ekonomi dalam ekspansi SIG di Vietnam, termasuk faktor keberhasilan, tantangan pasca-akuisisi, serta dampaknya terhadap daya saing dan performa pasar SIG secara regional dan global dari perspektif neoliberalisme, teori diplomasi ekonomi, konsep foreign direct investment (FDI), beserta Porter’s Diamond Model, dan konsep strategi manajemen bisnis internasional. Data dikumpulkan melalui studi pustaka, penelusuran daring, serta wawancara mendalam dengan pihak pengambil keputusan di SIG dan Thang Long Cement. Analisis dilakukan secara tematik dengan mengikuti tahapan umum dari teknik analisis data. Selain itu, analisis dilakukan menggunakan pendekatan analytic comparison dengan mengidentifikasi kesamaan pada kasus akuisisi serupa juga membandingkan performa SIG pada tahun 2016 dan 2023. Temuan penelitian ini menegaskan bahwa diplomasi ekonomi mendukung akses pasar dan investasi strategis dengan berbagai upaya pemerintah Indonesia, melalui perjanjian bilateral maupun verbal. Hasil menunjukkan bahwa akuisisi Thang Long Cement oleh SIG memperkuat posisi ekonomi Indonesia di Vietnam melalui efisiensi produksi, adaptasi lokal, dan kolaborasi strategis. Pada 2023, dengan kontribusi dari Thang Long Cement, SIG menguasai 50,5% pangsa pasar semen nasional. Analisis kasus ini pun menjadi referensi penting bagi pemerintah dan perusahaan dalam memperluas ekspansi bisnis internasional./The cement industry plays a crucial role in Indonesia's infrastructure development and economic growth. To expand its influence in Southeast Asia, Indonesia has implemented economic diplomacy strategies, one of which is the acquisition of Thang Long Cement in Vietnam by Semen Indonesia Group (SIG). This move strengthens Indonesia's position in the regional cement industry while enhancing its international competitiveness. This research analyses the role of economic diplomacy in SIG's expansion in Vietnam, including the factors contributing to its success, post-acquisition challenges, and its impact on SIG's competitiveness and market performance both regionally and globally. The analysis is conducted through the lens of neoliberalism, economic diplomacy theory, the concept of foreign direct investment (FDI), Porter’s Diamond Model, and the concept of international business management strategies. Data were collected through literature review, online research, and in-depth interviews with key decision-makers at SIG and Thang Long Cement. The analysis was conducted thematically, following the general stages of data analysis techniques. It also employed analytic comparison by drawing parallels with similar acquisition cases as well as comparing SIG's performance in 2016 and 2023. The findings highlight that economic diplomacy facilitates market access and strategic investments through various initiatives by the Indonesian government, including bilateral and verbal agreements. Results indicate that the acquisition of Thang Long Cement by SIG has strengthened Indonesia's economic position in Vietnam through production efficiency, local adaptation, and strategic collaboration. By 2023, with contributions from Thang Long Cement, SIG captured 50.5% of the national cement market share. This case study serves as a significant reference for both the government and companies seeking to expand their international business ventures.