(1633 – 5 September 1659) was the first wife and chief consort of Chhatrapati Shivaji Maharaj, the founder of the Maratha Empire. She was the mother of Shivaji Raje’s eldest son and heir-apparent, Chhatrapati Sambhaji Maharaj, who succeeded Shivaji Maharaj as the Emperor.
Saibai was a member of the prominent Nimbalkar dynasty. The members of the Nimbalkar dynasty were the rulers of Phaltan from the era of the Yadava dynasty until the integration of the princely states into the new nation of India in 1947. She was the daughter of the fifteenth Raja of Phaltan, Mudhojirao Naik Nimbalkar, and the sister of the sixteenth Raja, Bajaji Rao Naik Nimbalkar. Saibai's mother Reubai was from the Shirke dynasty.
In the year 1630, Mudhojirao ruled over Phaltan. Before that he was a prisoner of Adilshah at Satara Fort. Shahaji Raje (Shivray's father) helped him escape prison. Out of appreciation, Mudhojirao gave his daughter Sai to Shivaji Maharaj. The two of them got married in May of 1640.
The exact date of marriage is not known but Shivabharat mentions that it occurred after Shivaji Maharaj was in his teens. The wedding likely took place when Shivaji Maharaj was around 10–12 years old, and Sai Bai 7, around 1640-42 AD. A reference in Raja Shivachattrapati mentions the event to have taken place on 16 May 1640 AD, and that the marriage was conducted in Pune and Shahaji Raje was unable to attend it as he was in Bangalore at that time.
They had three daughters namely Sakhubai, Ranubai and Ambikabai followed by their son Sambhaji. On 7 September 1651, a girl was born to Shivaji Maharaj at Rajgad. She was named Sakvarbai (Sakhubai). She was later said to be of "wheatish" complexion and was extremely beautiful. Ranubai was their second daughter born in 1653. Ambikabai was their third daughter born in 1655. Chhatrapati Sambhaji Maharaj was their only son born on 14th may 1657 at Purandar fort.
Saibai and Shivaji Maharaj shared a close relationship; she was Shivray’s first and favourite wife. It is said that on his deathbed his last word was "Sai".
Saibai and Shivaji Maharaj had 4 children in total, three daughters and a son.
Their first daughter Sakhubai, was married to Mahadji the son of Bajaaji Naik Nimbalkar i.e. son of Saibai's brother. This marriage took place in year 1657 with an objective to consolidate Bajaji's return to Hinduism as he was converted to Islam by Aurangzeb.
Ranubai was married in Jadhav family. Amanika or Ambikabai married Harji Raje Mahadik in year 1668.
Saibai died at the age of 26 at Rajgad fort while Shivaji Maharaj was making preparations for his meeting with Afzal Khan at Pratapgad. She was ill from the time she gave birth to Sambhaji, who was two years old at the time of her death. He was brought up by Jijabai saheb, mother of Shivaji Maharaj. To nurture the newborn child Sambhaji, Jijabai appointed Dharai Gade Patil (Dharau) as his wetnurse.