MCM-41 mesoporous molecular sieve materials are synthesised using aqueous ammonia solution to adjust the pH of the reactant gel. Highly ordered MCM-41 with Si/Al ratio as low as 14 was obtained and characterised by Al-27 MAS NMR, XRD, N-2-adsorption, benzene sorption, and NH3-TPD measurements. The acidity of MCM-41 materials obtained in this system was conveniently generated through straightforward calcination of the as-synthesised sample. More mild acidic sites generated could be due to the avoidance of the multiple calcination procedure and/or the trace sodium species which are the poisons to Bronsted acid. The catalytic activities for n-heptane cracking and isomerization of m-xylene were investigated, and these were in accordance with the known properties of MCM-41.