The quantization of electric charge is the property due to which all free charges are integral multiple of basic unit of charge of an electron (or proton) represented by e.
The basic cause of quantization is that only integral no. of electrons can be transferred form one body to another on rubbing.
Eg. When 1 electron is transferred ,the charges acquired by the two bodies will be
q= ±1e = ±1.6 × 10^-19C