A method for preparing a conditionally active antibody, the method comprising: i. select a wild type antibody for an antigen； ii. develop the DNA encoding the wild type antibody using one or more evolutionary techniques to create a mutant DNA； iii. express the mutant DNA to obtain a mutant antibody； iv. subjecting the mutant antibody and the wild-type antibody to an assay in a normal physiological condition, which is within a normal range of the physiological condition at a conditionally active antibody administration site to a subject, or in a tissue or organ in a conditionally active antibody action site of a subject, and an assay under an aberrant condition, that deviates from the normal range of the physiological condition at the site of conditionally active antibody administration or in the tissue or organ at the site of action of the conditionally active antibody, wherein the normal physiological condition and the aberrant condition are the same condition selected for temperature, pH, osmotic pressure, osmolality, oxidation and electrolyte concentration； and V. select the conditionally active antibody from those mutant antibodies that exhibit both (a) a decrease in the activity in the assay in the normal physiological condition compared to the wild-type antibody, and (b) an increase in the activity in the assay in the aberrant condition compared to the wild type antibody.Un método para preparar un anticuerpo condicionalmente activo, comprendiendo el método: i. seleccionar un anticuerpo de tipo silvestre para un antígeno； ii. desarrollar el ADN que codifica el anticuerpo de tipo silvestre usando una o más técnicas evolutivas para crear un ADN mutante； iii. expresar el ADN mutante para obtener un anticuerpo mutante； iv. someter el anticuerpo mutante y el anticuerpo de tipo silvestre a un ensayo en una condición fisiológica normal, que está dentro de un intervalo normal de la condición fisiológica en un sitio de administración del anticuerpo condicionalmente acti
