In this work, the influence of P2O5 additive on the thermal expansion behaviour of sol-gel-derived cordierite was investigated by using XRD and coefficient of thermal expansion (CTE) measurement. The results showed that CTE value of the sample was greatly dependent on P2O5 addition, showing a zigzag trend. This phenomenon was related to the evolution of I-alpha(110)/I-mu(101) (the integral intensity of the (110) peak for alpha-cordierite and that of the (101) peak for mu-cordierite, respectively from X-ray diffraction spectra) in the investigated range, which was determined by the XMgO-P2O5 (X = 3, 2) compounds formed with the addition of P2O5.