The chemistry of silicon is largely that of four coordinated compounds but many stable compounds containing five and six coordinated silicon are known. Hypercoordinated silicon compounds attract interest from both the structural and reactivity point of view. The isolation of such compounds allows detailed insight into mechanistic pathways of nucleophilic substitution at silicon. On the other hand compounds based on such synthons exhibit interesting properties as electronic materials. Apart from the rich chemistry of these penta and/or hexacoordinate silicon compounds, it has been found that these species are relatively cheap, have low toxicity and are environmental friendly reagents. Therefore much of the research efforts, recently have been directed towards their synthesis, reactivity, structural investigations and biological activity of such compounds. The present paper deals with the overview of reactivity and biological activity of some penta and hexa-coordinated silicon compounds.