Sulphonates that work as emulsifiers in asphalt emulsification are generated in-situ by partial sulphonation of asphalt. More stable emulsions can be made by using sulphonated asphalt with a conventional emulsifier. To demonstrate, the sodium oleate was used as co-emulsifier. Effect of sulphonation time, temperature, acid concentration and amount of sulphonated asphalt on emulsion properties is studied. Use of 2 factorial design revealed that acid concentration, reaction time and temperature are significantly important parameters. The stability of emulsion increases with increased severity of reaction, that is, higher acid concentration, reaction time and temperature. In the most severe conditions, the asphalt forms coke-like polymerized matter that is not emulsifiable. The most stable emulsion was prepared with asphalt that was sulphonated at slightly milder conditions, namely, 69 °C, 60 minutes and 98 % acid. Storage stability, demulsibility and viscosity improved by 41.7 %, 46.8 % and 45.7 % respectively, with 40% of sulphonated asphalt.