Brexit is "destroying the country" but independence would be even worse, Lib Dem deputy leader Jo Swinson has warned the party's Scottish conference.
Ms Swinson told delegates in Hamilton that attempting to leave the EU after 40 years has brought "chaos".
And she said she "dreads to think" what attempting to leave the UK after 300 years would do to the country.
Lib Dem leader Vince Cable and Scottish leader Willie Rennie will speak at the two-day conference on Saturday.
The Lib Dems are holding the first of Scotland's spring party conferences, with the SNP, Conservatives, Labour and Greens all to follow in the coming months.
The party will debate topics including early years education, as well as Scotland's railways, prisons policy and trans rights over the two days.
While the Lib Dems and SNP both want another referendum on Brexit, Ms Swinson used her speech to warn that First Minister Nicola Sturgeon has "learned nothing" from the prime minister's attempts to secure a Brexit deal.
Ms Swinson said: "Every day as the chaos unfolds, we see how hard leaving the European Union will be. Every form of Brexit will make us poorer, it will put jobs at risk and it will weaken us on the global stage.
"What was supposed to be the 'easiest trade deal in human history' has proved to be anything but.
"Nicola Sturgeon and the SNP have learnt nothing from watching Theresa May negotiate our way out of Europe.
"Breaking a union of 40 years is destroying our country, I dread to think what dismantling a union of more than 300 years would do."
Ms Swinson also argued that the SNP should be concentrating on investing in education and mental health instead of "using Brexit to break up the UK".
Nicola Sturgeon has said that Brexit strengthens the case for Scottish independence, and has attempted to contrast an "outward looking" Scotland with an "isolationist" UK government.
Addressing a committee of the French parliament on Tuesday, she said independence would "see us recognising and embracing our interdependence with other nations".
Ms Sturgeon added: "We will always seek to be close allies and partners with our neighbours in Europe. The last two years, to my mind, have underlined the importance of that position."
The UK government has said it is committed to delivering on the result of the 2016 EU referendum, and wants to strike a deal which delivers for all parts of the UK.