Yellowfin tuna (Thunnus albacares) is one of large pelagic potential and economical species from the family of Scombridae. Production of yellowfin tuna from several potential fisheries areas (WPP) in Maluku was reported in the condition of overfishing. Meanwhile, tuna fisheries have been the potential resource for export demand. It is therefore, the status of yellowfin tuna fisheries should be monitored regularly following the regulation of PERMEN KP no 4 year 2017. The aims of this study were to measure the size of maturity of yellowfin tuna during October to December 2018 and utilize the empirical relationship to estimate optimum length and maximum length reached during this period. Observation on yellowfin tuna was conducted by joining local fishers from Kawa village, West Seram Regency. Handlines were occupied to catch yellowfin tuna around Banda Sea. From the catch sizes ranged from was 34cm to 168cm, the length maturity (Lm) of yellowfin tuna is 107.2cm of total length for female and 112.9cm for male. From the empirical relationship, the optimum length (Lopt) of yellowfin tuna during October-December 2018 was 120.5cm and maximum length (Lmax) was 181.4cm. This study showed that 90% of yellowfin catch was immature which indicated a recruitment overfishing. Only 2.4% of mega-spawners were caught during this study and indicated growth overfishing. Indication of an overfishing of the yellowfin tuna fishery contradicted to larger size of first maturity found. This contrary is discussed and balance fishing strategy is proposed as the idea to maintain the population of yellowfin tuna.