There is a profoundly subjectivist component to Kant's system of moral analysis because Kant states that we can only know things as they appear to us, not as they are in an objective reality. We are limited by the extent of our sensory perception. But we all also have a moral duty to do what is good. Humans have a conscience or inclination towards morality that is innate, and which Kant believed transcended the subjective nature of human perception. This desire to be moral and to use our free will for 'the good' is not subjective but is hard-wired into the human mind and soul.

Kant reconciled his belief in human subjective knowledge and the absolute obligation human beings have to do 'good' in his belief that intent is the most important thing to keep in mind when evaluating a moral action. For example, let us say that a man saves a swimmer from drowning, and soon after the swimmer kills someone in a drunken rage. This does not make the act of saving the man from drowning 'bad' given that the person who saved him could not have known the drowning individual's character. Our perceptions may be faulty and our knowledge may be incomplete, but the best thing to do is to act morally with the information we do in fact possess.

This is why Kant is not really a subjectivist. He does acknowledge that what we see, think, and believe is subjective...

However, how we use the data we have at our disposal to realize moral goods can be judged in absolute terms. Not every moral intention, when it is executed, will have a moral outcome, but that is how 'the good' in human beings should be evaluated. Moral imperatives should also be undertaken rationally, rather than out of emotion, to ensure that the individual is using the best information he or she can receive from his or her senses, and that subjective judgment is unclouded as possible. But merely because the moral actor strives to be objective, does not mean that every subjective aspect of reaching a decision can be completely eliminated.
Another anti-subjectivist component to the categorical imperative is its absolute nature. Every moral action must be undertaken as if that moral action stands for all time, no matter what the circumstances. There is no wavering from this stance in Kant. Thus, even when a subjective being undertakes an action, he is acting to set a standard, not merely perform a limited and singular action -- this flies in the face of traditional, subjective empiricism which looks on every action as an enclosed decision, and is irrelevant to similar instances that have occurred before and will occur later.