In this research the aim is to quantize the electromagnetic field near a dispersive and dissipative dielectric slab and then by using the explicit form of vector potential operator commutation relations, the Spontaneous emission rate of an atom (with definite electric dipole moment and transition frequency) is computed via Fermi’s golden rule. In the absence of any external sources of charges and current, because of the absorptive nature of the medium, a noise current density is added in frequency domain Maxwell equations. The noise current density is assumed to be an operator and satisfying a commutation relation proportional with the dielectric function imaginary part of medium. By using Maxwell’s equation and the standard definition of the vector potential Green function, the partial differential equations governing Green tensor components is derived and then by doing Fourier transforms they are reduced to nine ordinary differential equations in inverse space. By imposing a special rotation The symmetry in xy plane is removed and the electric field decomposes into a singlet and a doublet parts. The singlet part corresponds to the normal polarization state of electric field and the doublet part corresponds to the sum of parallel land longitudinal polarization states. Each part is quantized separately. In a gauge with zero scalar potential, by introducing the normal polarization vector the singlet part vector potential operator (in positive frequency domain) is derived in terms of Green tensor normal component and the normal component of the noise current density operator. Using the derived singlet part vector potential, the doublet vector potential operator is obtained in terms of other Green tensor components and the Cartesian components of the noise current operator. By computing Green tensor components the singlet and doublet vector potential operator can be obtained in terms of the right and left going annihilation operators. Using the commutation relations of