Plasma shaping effects on temperature gradient driven instabilities and geodesic acoustic oscillations are investigated with gyrokinetic theory and a local magnetohydrodynamic equilibrium model. In particular, we focus on the effect of the elongation κ, including its radial derivative sκ = (r/κ)(∂κ/∂r), in the large aspect ratio limit. An analytical formula of the dependence of the geodesic acoustic mode (GAM) frequency on the elongation is given. It is found that the GAM frequency sharply decreases with increasing elongation by the dependence of [(2 − αsκ)/(κ2 + 1)]1/2 with α = 0.5–1, which comes from the modification of ion classical polarization balanced by that of curvature drift polarization. The dependence of the critical threshold of the ETG/ITG instability on the elongation is numerically studied and a semi-analytical formula is given as (R0/LTc)/(R0/LTc)sκ=0,κ=1 = (1 + 0.36sκ)[1 + 0.11(κ − 1)], where R0 is the major radius and LTc is the critical scale length of the temperature gradient.