The Palace: The Lock Heart Jade

Luo Qing Chuan is a modern-day girl with a love of history who accidentally travels back in time to Emperor Kang Xi's era of the Qing dynasty. She becomes embroiled in the princes' struggle for the throne and is torn between her love for Yin Si, the eighth prince, and Yin Zhen, the fourth prince and future Emperor Yong Zheng. Caught in the crossfire of political intrigue, her wit and historical knowledge serve her well in her bid to stay alive as she begins to realize that true history is much darker and uglier than books portray.
(Source: DramaWiki)
~~ Adapted unofficially from the novel "Bu Bu Jing Xin" (步步惊心) by Tong Hua (桐华). ~~ Two versions available: 39 episodes (TV) || 35 episodes (DVD)