We present 29 mid-infrared spectra of the zodiacal light distributed over the sky. The observed 5.9-11.7 mu m spectral shapes are well represented by blackbody radiation with colour temperatures in the range of 255<= T<= 300 K. The spectra are smooth and featureless. The variation of the temperature can be explained by the geometrical distribution of dust in the inner solar system. This result indicates that although the interplanetary dust particles originate from discrete sources (comets, asteroids) the interplanetary cloud of today seems to be well mixed in terms of grain composition and size distribution. Based on observations with ISO, an ESA project with instruments funded by ESA member states (especially the PI countries France, Germany, The Netherlands and the UK) with participation of ISAS and NASA.