The present invention relates to a photosensitive resin composition excellent in pliability, ultraviolet sensitivity for development, developability with an aqueous alkali solution, and storage stability at room temperature and a circuit substrate employing the same. The photosensitive resin composition includes a siloxane-containing polyamic acid resin having structural units respectively represented by the following formulae (1), (2), and (3) and a photopolymerization initiator incorporated therein. The circuit substrate is coated with the photosensitive resin composition. In the formulae, Ar represents a residue of an aromatic tetracarboxylic acid; R1 represents alkyl group having 1 to 6 carbon atoms or phenyl group; R2 represents alkylene group having 2 to 6 carbon atoms or phenylene group; l represents a number of 0 to 10; R3 represents a divalent group or a direct bond; R4 represents —CH2═CH—R6—, in which R6 represents a direct bond, alkylene group having 1 to 6 carbon atoms, or phenylene group; R5 represents a diamine residue; and m, n, and o, indicating the range of the abundant molar ratios of the respective structural units, are 0.3 to 0.95, 0.05 to 0.7, and 0 to 0.5, respectively.