Litopenaeus vannamei is one of the most well-known fishery products and has high market value. In contrast, production of vannamei shrimp is facing threats from several diseases caused by bacteria, virus, and even parasites that attack the shrimp immune system. The purpose of this study is to identify the immunomodulatory effect of Eucheuma serra extract to enhance haemocyte cells production in Litopenaeus vannamei as the non-specific internal immune substance. The research method used was a complete randomised design with 5 concentrations of injected Eucheuma serra extract treatments and one placebo as control. Eucheuma serra extract administered on shrimp abdomen and the haemocyte cell samples collected from shrimp on day 0 and day 6. Treatment using 8 ppm injected Eucheuma serra extract showed the highest haemocyte cell amount increase about 15.90 million cells/ml in 6 days after injection. Statistical calculation using ANOVA test showed a significant difference in the amount of haemocyte cell at before and after treatment.