In the last years, the potential of NIRS for quantitative and qualitative analysis of olives fruits and oils has been investigated. However, limited work has been published about the on-line implementation of NIR spectroscopy in this sector. NIRS application at factory level (olive mills) is desirable. However, prior its implementation, many parameters related to the on-line spectrum acquisition, must be studied and optimised. In this paper, the influence of parameters such as focal distance and integration time has been studied. On-line spectral measurements were performed on intact olives in the spectral range of 380-1690 nm using a diode array spectrometer located on the top of a conveyor belt. The statistical criteria used to evaluate the spectral repeatability for each level of parameters considered were the standard deviation (SD) of the log (1/R) values and the root mean square statistics (RMS). Results demonstrated that for on-line control of olives in movement, spectra acquisition process was more affected by the focal distance chosen than by the integration time used. A focal distance of 13 mm and an integration time of 5 s have been defined as the optimal operational conditions. (C) 2012 Elsevier Ltd. All rights reserved.