To provide a steel material to be hydroformed which has superior hydroformability, superior weldability and a tensile strength of 390 MPa or higher.

The steel material to be hydroformed has a chemical composition comprising 0.02-0.35% C, 0.01-1.0% Si, 0.01-2.5% Mn, 0.005-0.10% P, S≤0.0100%, 0.001-0.1% Al, 0.005-0.020% Ti, 0.0004-0.0100% N, and the balance Fe with impurities; includes crystallization-type TiN-based particles with particle diameters of 0.3 μm or larger in an amount of 50 to 50,000 particles per 1 mm2of a cross section, while the whole crystallization-type TiN-based particles have an average particle diameter of 7 μm or less; and includes such ferrite as to occupy 50% or more by an area rate in a structure and have an average diameter of 3 to 30 μm. The steel material may include one or more groups among the following groups (a) to (d): (a) one or more elements of 0.1% or less Nb and 0.2% or less V; (b) one or more elements of 1.0% or less Mo, 1.0% or less Ni and 1.0% or less Cu; (c) one or more elements of 1.0% or less Cr and 0.0005-0.003% B; and (d) 0.0002-0.01% Ca, 0.0002-0.01% Mg and 0.0002-0.01% REM.

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