KAI1, also known as CD82, has been shown to have a potential impact on the invasiveness of cancer cells. In the present study, expression pattern of KAI1, both at transcription and translation levels and the potential clinical value of the expression were explored in a cohort of normal and ductal mammary cancer tissues (n=71). A marked reduction of KAI1 transcript was observed in invasive ductal breast tumours as compared to normal tissues. Expression of KAI1 protein was higher in normal tissues as compared to tumour samples. Though no significant difference of KAI1 expression between different grades of tumour was observed (p=0.064), significant correlation of TNM staging with KAI1 expression has been observed in invasive ductal breast cancer patients (p=0.045). Additionally, it was also observed that patients showing higher expression of KAI1 had a longer 10-year survival rate as compared to a low level or completely negative expression KAI1 (p=0.0136). KAI1 inverse correlation with tumour progression may be used as a strong prognostic marker.