In May alone, according to the regulator CNMC, the number increased by 107,607, and as of this May Movistar accounted for 2.6 million, or 67.7%, of the total number of lines.
At the same time, the number of DSL lines fell by 1.4 million in the year to May.
Movistar claimed a 43.75% share of the fixed broadband market in Spain this May.
It was followed by Orange (28.64%) and Vodafone (22.65%), with other providers claiming the remainder (4.96%).
The total number of fixed broadband lines stood at 13,368,134, equivalent to 28.8 per 100 inhabitants.
This was up from 27.6 a year earlier.