A new non-rubbing alignment film for nematic liquid crystals has been developed employing the polyimide precursor Langmuir-Blodgett film having long chain alkyl groups. This film has the ability to tilt the liquid crystal molecules. We discovered that the pretilt angle of nematic liquid crystals can be controlled by changing the thermal treatment temperature of the polyimide precursor Langmuir-Blodgett films. We studied the causing mechanism of the pretilt angle by investigating the thermal treatment temperature dependence of degree of imidization, the number of the long chain alkyl groups, the critical surface tension, and the tilt angle of long chain alkyl groups of the Langmuir-Blodgett films.