A method of manufacturing a neutral and transparent metal oxide colloid solution containing dispersed titanium dioxide nano particles comprising the steps of (i) adding a titanium compound and a stabilizer to alcohol to produce a titanium-containing solution and (ii) neutralizing the titanium-containing solution of step (i) by adding a basic solution to produce a neutralized solution with the pH of the neutralized solution in a range of 6-8; and (iii) heating the neutralized solution at a temperature of above 75.degree. C.