Density functional theory has been used with different combinations of exchange and correlation functionals to study the proton affinities of six organic-molecules, namely H2CO, CH3CHO, CH3OH, C2H5OH, HCOOH, and CH3COOH. Complete geometry optimizations have been carried out for both the neutral and protonated species with all combinations of functionals. The proton affinity values are then compared with the corresponding experimental values. It has been observed that combination of Perdew’s and Becke’s exchanges with Proynov’s correlation functional is the most effective in reproducing the proton affinity.