Using the data taken by the ARGO-YBJ experiment (606 $g/cm^{2}$, Tibet, P.R.China) in the period of July to September 2006, the first measurement of EAS size spectrum in the range of $N_{e}=5\times10^{4}-5\times10^{6}$ is presented at different zenith angles. The attenuation and absorption lengths have been determined by applying different analysis methods. Furthermore the proton-air inelastic cross section around few hundrend TeV is explored by using the factor $k=\lambda_{abs}^{sim}/\lambda_{pair}^{sim}$ obtained on the base of Monte Carlo simulation.

ARGO-YBJ Collaboration

Proceedings of the 30th International Cosmic Ray Conference; Rogelio Caballero, Juan Carlos D'Olivo, Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sánchez, José F. Valdés-Galicia (eds.); Universidad Nacional Autónoma de México, Mexico City, Mexico, 2008; Vol. 4 (HE part 1), pages 135-138