Ultrafine aerosol particles (UFAP, diameter < 100 nm) emitted from laser printers have been considered as toxic aerosol. To address the response relationship between the operating parameters and real-time ultrafine emissions, three commercial printers were used to experimentally investigate their emission characteristics under different operating parameters including: the ready process, the number of pages printed, the page coverage and the print mode. The results showed that ultrafine particle emissions varied with the printer model. No causal correlation existed between the ultrafine particle number concentration and the PM2.5 mass concentration of a specific printer. Ultrafine particle emission characteristics were highly associated with operating parameters other than printer/cartridge toner model. Not all of the tested printers displayed ultrafine particle emissions in the ready process. Ultrafine particle emissions increased with increasing number of printed pages and page coverage with a nonlinear relationship. Compared with continuous printing, intermittent printing has a so-called “peak-shaving” or “peak-shift” effect. The results may help to provide a simple and effective way to control and reduce ultrafine particle emissions from laser printers by means of improvement of operating conditions.