The present invention relates to an eco-friendly turf protectant using seawater, which does not have side effects such as toxicity and is effective in turf growth, and to a manufacturing method thereof. The manufacturing method of the present invention comprises: a standing step of standing seawater； a first concentrated seawater preparing step； a second concentrated seawater preparing step； a third concentrated seawater preparing step； a fourth concentrated seawater preparing step； a fifth concentrated seawater preparing step； an inoculation step of inoculating microalgae； a sixth concentrated seawater preparing step； a first mixing step； a seventh concentrated seawater preparing step； an eighth concentrated seawater preparing step； a second mixing step； a ninth concentrated seawater preparing step； and a third mixing step.본 발명은 독성 등의 부작용이 없고 잔디 주변의 여러종류의 잡초 등을 신속히 제거하고 효과도 장기간 지속되어 잔디의 생육에 효과적인 해수를 이용한 친환경 잔디 보호제를 제공한다.
