The present paper reports the analysis and the antimicrobial activity viz. antifungal activity of some pyrazolone compounds which were performed against Alternaria solani using disc diffusion method on nutrient agar and nutrient broth media. The compounds were characterized by elemental analysis and spectral studies. Result of antimicrobial screening indicated that compounds 4-Amino antipyrine thiosemicarbazone, 1-(2-Chloro-5-sulfophenyl)-3-methyl-5-pyrazolone and 1-(4 -Sulfoamidophenyl)-3-methyl-5-pyrazolone were found to be the most potent/active against A. solani. Correlation studies between different computed properties of the compounds with their biological activity, QSAR (Quantitative Structure Activity Relationship) investigations with a stepwise linear regression analysis were conducted. The studies are carried out using Hyperchem 8.0 version software using AM1, PM3, MNDO and ZINDO methods. Selected QSAR/ 3D-QSAR equations including different physical parameters of these series are reported.