We present the high-resolution (R~=60000), high signal-to-noise ratio (S/N~=120) spectroscopic analysis of 12 red giant members of the Galactic open cluster NGC 6940. We applied Yonsei-Yale isochrones to the colour-magnitude diagram, which suggested an age of 1.1Gyr for the cluster with a turn-off mass of 2 M_{sun}_. Atmospheric parameters (T_eff_, logg, [Fe/H], and {xi}_t_) were determined via equivalent widths of FeI, FeII, TiI, and TiII lines. Calculated mean metallicity of the cluster is <[Fe/H]>=0.04+/-0.02. We derived abundances of {alpha} (Mg, Si, Ca), Fe-group (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and n-capture (Y, La, Nd, Eu) elements to be about solar. Light odd-Z elements Na and Al are slightly enhanced in MMU 108 and MMU 152 by ~0.34 and ~0.16dex, respectively. Abundances of light elements Li, C, N, O, and ^12^C/^13^C ratios were derived from spectrum syntheses of the LiI resonance doublet at 6707{AA}, [OI] line at 6300{AA}, C_2_ Swan bandheads at 5164 and 5635{AA}, and strong ^12,13^CN system lines in the 7995-8040{AA} region. Most carbon isotopic ratios are similar to those found in other solar-metallicity giants, but MMU 152 has an unusual value of ^12^C/^13^C=6. Evaluation of the LiCNO abundances and ^12^C/^13^C ratios along with the present theoretical models suggests that all the red giants in our sample are core-helium-burning clump stars.