Fumarolic gases, rocks and condensate samples from Merapi volcano (Indonesia) have been analyzed by multiple collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for their Zn isotopic compositions. The variation observed, expressed as delta Zn-66 (delta Zn-66 = [(Zn-66/Zn-64)(sample)/(Zn-66/Zn-64)(JMC) (3-049L)-1]10(3)), ranges from+0.05 parts per thousand. to + 1.68 parts per thousand.. The overall reproducibility was found to be better than 0.10 parts per thousand. (2SD). The delta Zn-66 of andesitic rock samples are homogeneous with a mean value of +0.24 parts per thousand., which is comparable to previously reported basalt data. delta Zn-66 in the Woro furnerolic field are ranging from +0.05 parts per thousand to +0.85 parts per thousand and +1.48 parts per thousand to +1.68 parts per thousand in fumarolic gases and condensates respectively. Upon cooling from 590 to 297 degrees C, gaseous Zn concentrations decrease and become increasingly enriched in the lighter Zn isotopes, while the condensates become increasingly enriched in the heavier isotopes. Gas and condensate isotopic compositions can be explained with a Rayleigh condensation model with temperature dependent isotope fractionation factor, alpha((solid/vapor)). Over the 574 degrees C to 297 degrees C range of observations, 1000 In(alpha(solid/vapour)) C-1+C-2/T+C-3/T-2 (with C-1=0, C-2= -0.88 x 10(3), C-3 = 1.00 x 10(6) and T in degrees Kelvin), which corresponds to alpha((solid/vapor)) of 1.00033 to 1.00153 respectively at the indicated temperatures. (c) 2008 Elsevier B.V. All rights reserved.