Reduce exported .obj file size I am new to Blender, 
I have created a 3D object model for my project. My .obj file (exported from) Blender is too large, around 41 MB. How can I reduce its size? I have to use it in three.js
Since its size is too large, it is taking too much time to load.
You will have to reduce the number of polygons (vertices, edges and faces). My guess is that you have a pretty high poly model to generate a 41mb file.

One way to reduce a mesh's polygons is to use a Decimate modifier. Do note that you will have to apply the modifier before is takes effect on the export.