HONG KONG—A Chinese startup backed by Ant Financial Services Group, the finance affiliate of e-commerce giant Alibaba Group Holding Ltd., is planning an initial public offering in the U.S., according to people familiar with the matter.

Beijing Happy Times Technology Development Co., which lets university students pay for online purchases in installments through its popular Qufenqi loan product, has begun preliminary work with Citigroup Inc., China International Capital Corp., Credit Suisse Group AG and Morgan Stanley on an...