Oxide glasses with composition $35P_2O_5 (45-x)V_2O_5 xAs_2O_3 20Fe_2O_3$ ($0 \le x \le 25$ mol %) have been prepared by the conventional melt quenching technique. The glassy state of the as prepared samples is characterized using X-ray diffraction (XRD) and differential thermal analysis (DTA). In order to understand the effect of $As_2O_3$ contents on the structure and the structural changes occurring in these glasses, the density, $\rho$, and molar volume, $V_m$, measurements have also been made. The density increases and molar volume decreases with increasing $As_2O_3$ contents. The dc conductivity decreases with increasing $As_2O_3$ contents. The room temperature dc conductivity is typically $10^{-5} - 10^{-9}\,S\,cm^{-1}$ with activation energy $0.28 - 0.49\,\text{eV}$. Two glass transition temperatures, $T_{g1}$ and $T_{g2}$, are detected at the DTA traces of the investigated glass system. From the dependence on heating rates of $T_{g1}$, $T_{g2}$, and $T_p$, the activation energies for glass transitions, $E_{g1}$, $E_{g2}$, and the activation energy for crystallization, $E_c$, are calculated. All the results confirmed that the thermal stability increases with increasing $As_2O_3$ contents in the investigated glass system. The glass sample with $x = 25$ (mol %) is of the highest glass thermal stability $\Delta T_x = 207 \pm 2\,\text{K}$ at $20\,\text{K/min}$ heating rate and crystallization activation energy $E_c = 224.5 \pm 3\,\text{kJ/mol}$.