In my company there is a uniform policy only for male employees, whereas female employees are there and not wearing uniforms. How can I convince my boss to implement a uniform policy for all employees, including women?
The first step in challenging a policy is to understand it. Start by asking why there is a different policy for women than for men. There may be good reasons (different job requirements, availability of suitable uniforms, relative cost, industry expectations, holdovers from prior management, or preference expressed by employees in each group).
It is unclear what the basis of your objection is. If you don't like having to wear a uniform, then the fact that women are not required to wear them is an argument in your court for abolishing them for men. If you like wearing a uniform, then it shouldn't matter to you whether others are required to wear them or not, unless there is some reason that their lack of a uniform is impacting your work.
Sometimes the only reason we are objecting to something is that it just seems "unfair." I would suggest to you that unless this policy regarding women's dress is impacting your work, you might let go of the need for and expectation of "fairness." Fairness is relative; nothing is ever absolutely fair or equal. In pushing for it over an issue that does not impact you, you risk alienating coworkers and creating a divide amongst staff. Asking for a change regarding your own dress requirements makes sense here; asking for a change regarding the dress requirements of others is likely to be seen as an overstep.