We established new human breast cancer cell line, OCUB-1 derived from the pleural effusion of 53-year old female with recurrent breast cancer. Two sub-cell lines were also established with cloning technique from OCUB-1. Investigating the differences of characteristics between OCUB-1M and 1F, OCUB-1M shows a monolayered growing and OCUB-1F grows in floating. OCUB-1M and 1F revealed Modo 84 and 41 by chromosomal analysis and flow cytometric analysis showed OCUB-1M had twice amount of DNAs as -1F. OCUB-1M revealed higher expression of E-cadherin and laminin receptor against-1F, and activity of 92kDa type IV collagenase could be seen only in OCUB-1M. Estorogen and progesteron receptor were negative in either OCUB-1M and -1F, and no production of tumor markers in the spent media (CEA, CA19-9, CA15-3 and NCC-ST439) was detected in both cells. Both cells could be hetero-transplanted in nude mice, but they showed different histology.