The polyculture system was used to increase the productivity of extensive brackishwater ponds to produce optimal agar with varying densities of three commodities: milkfish, Vannamei shrimp, and Gracilaria verrucosa. This study aims to obtain the optimal density of the three commodities in extensive brackishwater ponds with polyculture systems to produce the best agar quality for G. verrucosa. The research was conducted in the expanse of the Polyculture System Extensive brackishwater Pond in Lamongan Regency. The study used a Completely Randomized Design (CRD) with 3 density treatments (milkfish m-2 : Vannamei shrimp m-2 : G. verrucosa g m-2) and 3 replicates: A (10:10:250), B (20:20:500), and C (30:30:1000). Statistical analysis uses one way ANOVA (Analysis of Variance), while Tukey's HSD (Honestly Significant Difference) and Path Analysis use Pearson Correlation. The results showed that the best density obtained in treatment A gave a significant difference from treatments B and C in producing Specific Growth Rate, Absolute Weight, Absolute Length, Carbon Content, and quality of agar rendementing the best of seaweed G. verrucosa. From the path analysis, CNP nutrients and the growth of G. verrucosa seaweed have a strong and very strong influence to improve the quality of agar rendementing G. verrucosa seaweed.