A quantitative structure–property relationship (QSPR) study was performed for prediction of enthalpies of 134 acyclic alkanes using modified Xu (mXu) index and atom-type-based AI topological indices. At first, a simple linear regression model was developed using mXu index alone and the statistics were R2 = 0.947, F = 2335 and standard error of 1.00. The results showed that combination of the atom-type-based AI topological indices and mXu index can produce significant improvement in the statistical quality of the model, especially the decrease in the standard error was 33% relative to the simple linear model. The final model was validated to be statistically significant and reliable using external validation technique. External validation was performed by dividing the entire data set into three subsets and predicting enthalpy values for each subset from the other two as training sets. Average standard error of calibration of 0.66 and average standard error of prediction of 0.68 demonstrated the validity and good efficiency of the topological indices in modeling enthalpies of alkanes. The obtained results showed that the enthalpy for acyclic alkanes is dominated by molecular size and the atomic groups are also important although their contributions are much smaller than that of the molecular size.