Vapor-liquid equilibria of 1-butanol+ethanol and isoamyl alcohol+ethanol systems containing a minute amount of crotonaldehyde were measured at atmospheric pressure using an Othmer-type still. Equilibrium ratio curves of the trace component (crotonaldehyde) are shown to exhibit a characteristic shape. Batch rectification experiments of ethanol, 1-butanol, 1-butanol+ethanol and isoamyl alcohol+ethanol systems containing 0.1 wt% crotonaldehyde were carried out using a glass Oldershow-type column. The lowering of the concentration of the trace component in distillate becomes gentle with the progress of distillation. The distillation curves of the trace component are found to show a peak at the change of distillate of the major components. In the residue of batch rectification of l-butanol and isoamyl alcohol solutions, crotonaldehyde was detected in much higher concentration than in the last distillate.