An experiment was carried out to study the nutritional requirement and response of different physiological parameters viz., temperature and pH on mycelial growth of different isolates of Alternaria porri (Ellis) Cif causing purple blotch of onion. The five different pH levels, temperature, carbon sources and nitrogen sources were tested for their effect on mycelial growth and sporulation of A. porri. The results showed that the maximum mycelial growth and sporulation of A. porri was observed at pH 7.0 and minimum at pH 9.0. In temperature range the maximum mycelial growth and sporulation was recorded at 30 oC and minimum at 10 o. The mycelial growth of A. porri was different on Czapek’s dox agar basal medium with different carbon sources. Maximum radial growth was observed on maltose followed by sucrose and minimum on dextrose maltose. The mycelial growth of A. porri grown on varied Czapek’s dox agar basal medium with different nitrogen sources. Maximum mycelial growth and sporulation was observed on potassium nitrate followed by sodium nitrate and minimum on urea, respectively.