What should I do if I like a mature female colleague in her forties at work?

First of all, it needs to be clear that feelings are personal inner things and cannot be influenced by others. However, there are some suggestions to help you deal with this situation.

1. Respect her feelings: If you have expressed your feelings to her, but she doesn't respond or agree, then you need to respect her decision. Don't try to force or pressure her.

2. Be professional: No matter how you feel about her, you need to be professional and respect her. Don't be too intimate or too enthusiastic at work.

3. Know her situation: If you don't know her marital status or whether she has a partner, then you need to find out this situation first. If she already has a partner, you need to respect her choice and don't try to interfere or destroy her relationship.

4. Establish friendship: You can try to establish friendship with her before expressing your feelings. Understand her hobbies, professional background and so on, so as to better understand her and increase the trust and interaction between you.

5. Consider the consequences: If you decide to confess to her, you need to consider the consequences. If she rejects your feelings, you need to be prepared to face this situation and don't let it affect your work and career development.

Last but not least, no matter what action you take, you need to respect her feelings and decisions. If she is unwilling to respond to your feelings, you need to respect her choice and continue to be professional and friendly.