This invention discloses a steel cord. The steel cord comprises a plurality of strands twisted together with a cord twist pitch. Each strand comprises a plurality of filaments twisted together with a strand twist pitch. The elongation at break of the steel cord is no less than 5%. The strand comprises a strand twist angle. The steel cord comprises a cord twist angle. When the sum of the strand twist angle and the cord twist angle is between 20 and 29 degree, the structural elongation of the steel cord is no less than 2.0%. When the sum of the strand twist angle and the cord twist angle is between 30 and 38 degree, the structural elongation of the steel cord is no less than 2.5%. When the sum of the strand twist angle and the cord twist angle is between 39 and 48 degree, the structural elongation of the steel cord is no less than 3.0%. Preferably, the structural elongation of the steel cord is no more than 4.0%. The steel cord has high elongation at break, high structural elongation and high rubber penetration. This invention also provides a pneumatic tire comprising the steel cord mentioned above.