The π, π∗ absorption spectrum and its solvent effect of 2-methyl-l-indenone have been found to be similar to those of lj2-naphthoquinone. This fact is discussed on the basis of the results calculated using the P-P-P method. The similarity of the calculated 7r-electronic structures in the low-energy π, π∗ singlet states between 1-indenone and 1,2-naphthoquinone is not so good as that between fluorenone and 9,10-phenanthrenequinone.