In the present study, Al2O3 coated on macro-porous silicon (m-PS) is prepared by atomic layer deposition (ALD) whereas m-PS is prepared by electrochemical anodization of P type silicon (100) with current density of 15 mA/cm2. Field emission scanning electron microscopy analysis shows Al2O3 nanoparticles with size of ~ 100 nm are conformally coated on m-PS. The surface chemistry and formation mechanism of ALD of Al2O3 (ALD-Al2O3) on m-PS are demonstrated in detail. Optical profilometer results of Al2O3/m-PS confirm conformality of Al2O3 coating on m-PS because the surface amplitude parameter values of m-PS are decreased after ALD-Al2O3. Fourier Transform Infrared analysis confirms that unstable Si-H species of m-PS are replaced with stable Si-Al species. X-ray photoelectron spectroscopy (XPS) analysis of Al2O3/m-PS is carried out for chemical analysis and band gap energy measurement of Al2O3. The XPS survey spectrum shows that fluorine peak is also evolved along with Al, O and C elements which confirm that m-PS surface consists of fluorine. The band gap energy of Al2O3 coating is calculated as 6.91 eV from analysis of high resolution O 1s spectrum.