I did hair transplantation through FUE, a year ago. Why did my transplanted hairs turn curly?

It is not normal for transplanted hair to change from straight to curly.  It would be best to follow up with your doctor for an examination.

Dear Muhammadimran, Thank you for your question. I would encourage you to discuss these concerns with your original surgeon. They will be able to evaluate and examine you, which will help them provide a more authoritative answer. Let me know if you have any further questions or concerns. Good luck! P. Daniel Ward, MD. 

On occasion, we see grafts that grow that are a bit different than the surrounding native hairs or different than expected. Sometimes, with graft growth and maturation, they look more like the surrounding hairs. It's tough to say what's really going on here, so go back to your surgeon for a look. In the meantime, support your results by keeping up with the nonsurgical hair saving techniques, such as topical Minoxidil and oral finasteride. PRP is a very important adjunct too. 

some people will see a change in the curl of their hair towards mor ecorly. Most people like this unless the curl is a kink