Gracilaria is one of valuable and demanding aquaculture commodities in Indonesia. The purpose of the study was to know and understand the cultivation of seaweed Gracilaria sp. The study was done from 6 February 2017 until 6 May 2017 in Domas Village, Pontang, Serang, Banten. Data on management, technical, and financial were collected by attending seaweed farmer’s culture activities and interviewing them. Observed site was specifically located at Crocoh, Kali Domas and Teluk. There were 33 ponds of polyculture between Gracilaria and milkfish. The average growth rate of seaweed cultured by farmer in Crocoh and Kali Domas were 1,95% and 1,53%, respectively. Meanwhile in Teluk region had growth rate of 3%; 2,1% and -32%. Result of final biomass relative to first sown seed biomass (100 gram) of treatment of spreading every 2 weeks, 3 weeks, and control (without spreading) were 9 fold, 8 fold, and 5 fold. The result of measurement of several water quality parameter were temperature 29-39˚C, salinity 0-31 g/l, pH 6-8, nitrate 0-50 mg/l, phosphate 0,1-2 mg/l, and potassium 200-420 mg/l. Most of the ponds had light penetration until buttom of the pond with the depth of the water about 9-50 cm. Daily duration to add water was 4 hours at night and 3 hours in early morning to throw water. Pests and diseases found during study were Hypnea muscoformis, Achanthopora, Chaetomorpha, Lingbya, Siganus sp., Lates calcalifer, Sillago sihama, and ice- ice. The polyculture between Gracilaria and milkfish was feasible to be continuesly developed because it had average of investment Rp 3,900,350,-; fixed cost Rp17,468,739,-; variable cost Rp45,632,919,-; profit Rp34,100,258,- with four ponds suffered losses, B/C ratio 1.65; BEP (unit) 16,828 kg, BEP (price) Rp94,235,182,-; PP 55 years 6 months and ROI 5.3%.