As you can travel from Ljubljana to Split you can obviously travel the other way.

The German rail website:

bahn.de/international/view/e...

lists almost all European train times & details. It will give you train times, but not fares. For those you will have to try the Croatian railway website (in English):

hznet.hr/iSite3/Default.aspx...

It's a long journey: fastest is 8+ hours.

You may be able find bus times & fares here:

http://www.autotrans.hr/index.php?lan=1

which is the Croatian Eurolines company.

I can't find any departure times for Ljubljana on the Split bus station site:

ak-split.hr/EN/vozni.red/ind...

There is no bus that goes directly from Split to Ljubljana. You will have to go by bus to Rijeka and then take either the train (2 a day, current timetable dep 12.57 arr 15.25 and dep 20.45 ar 23.22) or a bus if you can find one.

Here's the current timetable for daily buses from Split to Rijeka, giving departure and arrival times, the platform the buses leave from at the main bus station and the compnay

05:00 12:30 1 BRIONI d.d.PULA
08:00 16:30 1 LARUS d.o.o.ZADAR
09:00 17:39 1 AUTOTRANS RIJEKA d.o.o.RIJEKA
11:00 19:20 1 AUTOTRANSPORT d.d.ŠIBENIK
13:00 20:40 1 AUTOTRANS RIJEKA d.o.o.RIJEKA
15:00 22:59 1 AUTOTRANS RIJEKA d.o.o.RIJEKA
20:30 04:00 1 AUTOTRANS RIJEKA d.o.o.RIJEKA
21:30 04:30 1 AUTOTRANS-AUTOTRANSPORT ŠIBENIK
22:00 05:37 1 AUTOTRANS RIJEKA d.o.o.RIJEKA

It's about a kilometres from the bus station to the train station in Rijeka. The buses keep very god time in Croatia so your best bet looks to be the 0900 or 1100 departure to catch the 2045 train

Here's the Autotrans bus company website - they may have a bus - you could try contacting them via email or a phone cal if you don't have any success with the timetable

[original link]

You can go via Rijeka as the previous poster said, but if I just wanted to get from Split to Ljubljana without stopping along the way, I'd probably go via Zagreb. Either train or bus to Zagreb, journey time 5-6 hours (make sure to get an express service if you go by bus), then train to Ljubljana (2.5 hours). See [original link] for train times, [original link] for buses to Zagreb.