In his Lunar New Year message, Mr Lee said the wealthy city-state needed "enough children to form the next generation" amid concerns over the influx of immigrants.
"Unfortunately, despite our efforts to promote marriage and parenthood, our birth rates are still too low," Mr Lee, a father of four, said.
Mr Lee said Singapore's current fertility rate is 1.19 babies per female, down from 1.29 in 2012. The rate for ethnic Chinese Singaporeans, who make up 74% of the resident population, is lower, at 1.06.
"We must try to do better. I hope the Year of the Horse will see some improvement," he said.
The 61-year-old leader noted that Valentine's Day this year would coincide with the auspicious 15th day of Lunar New Year festivities known as "Chap Goh Mei".
"Almost 300 couples have registered to marry on this auspicious day, so we are off to a galloping start," he said.
"I hope to hear more wedding bells and newborns’ cries throughout the year."
Despite a series of so-called "baby bonuses" to encourage couples to have children, Singapore has not been able to boost its fertility rate to the 2.1 level needed to maintain the native-born population.
Its low birth rate has forced the government to rely on foreign workers. Foreigners now comprise a third of the 5.4 million population.
The influx, however, has sparked protests and prompted the government to tighten immigration flows in recent years.
Ethnic Chinese around the world on Friday will usher in the Year of the Horse.