Investigation on the relative condition factor (Kn) and carapace length (CL mm) weight, (W g) relationship of  'Udang windu'  Penaeus monodon FABRICIUS was carried out at Segara Anakan mangrove waters, Cilacap from December 1982 to November 1983. The relationships for males, females and combined were found to be; W♂- 10^-3 5.0761 L^2.3598,  W♀- 10^-3 5.1485 L2.³⁵²⁵, and W comb. = 10-'5.1832 L^2.3521 respectively. The values of relative condition factor was found to be highest in smaller shrimp 21.0-25.0 mm CL of both sexes. High values of Kn were obtained up to 1.372 in males and 1.490 in females respectively.