We present the high-resolution (R a parts per thousand 60 000), high signal-to-noise ratio (S/N a parts per thousand integral 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 1.1 Gyr for the cluster with a turn-off mass of 2 M-aS (TM). Atmospheric parameters (T-eff, log g, [Fe/H], and xi(t)) were determined via equivalent widths of Fe i, Fe ii, Ti i, and Ti ii lines. Calculated mean metallicity of the cluster is aEuro[Fe/H]aEuro parts per thousand = 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 similar to 0.34 and similar to 0.16 dex, respectively. Abundances of light elements Li, C, N, O, and C-12/C-13 ratios were derived from spectrum syntheses of the Li i resonance doublet at 6707 , [O i] line at 6300 , C-2 Swan bandheads at 5164 and 5635 , and strong (CN)-C-12,13 system lines in the 7995-8040 region. Most carbon isotopic ratios are similar to those found in other solar-metallicity giants, but MMU 152 has an unusual value of C-12/C-13 = 6. Evaluation of the LiCNO abundances and C-12/C-13 ratios along with the present theoretical models suggests that all the red giants in our sample are core-helium-burning clump stars.