Google the wikipedia article “Comparison of Poruguese and Spanish”, it has links to valid references if you doubt the write up.
_Portuguese and Spanish, although closely related sister languages, differ in many details of their phonology, grammar and lexicon. Both are part of a broader language family known as West Iberian Romance, which also includes several other languages or dialects with fewer speakers, all of which are mutually intelligible to some degree. A 1949 study by Italian-American linguist Mario Pei, analyzing the degree of difference from a language’s parent (Latin, in the case of Romance languages) by comparing phonology, inflection, syntax, vocabulary, and intonation, indicated the following percentages (the higher the percentage, the greater the distance from Latin): In the case of Spanish it was 20%, the third closest Romance language to Latin, only behind Sardinian (8% distance) and Italian (12% distance). Portuguese was 31%, making it the second furthest language from Latin after French (44% distance).
The most obvious differences are in pronunciation. Mutual intelligibility is greater for the written languages than for their spoken forms. Compare, for example, the following sentences:
Al buen entendedor pocas palabras bastan (Spanish: [al ˈβ̞we̞n e̞nte̞nde̞ˈð̞o̞r ˈpo̞kas paˈlaβ̞ɾaz ˈβ̞astan])
Ao bom entendedor poucas palavras bastam (European Portuguese: [ɜw ˈβõ̞(ɰ̃) ẽ̞tẽ̞dʊ̜̆ˈðoɾ ˈpo(w)kə̻̆ɕ pə̆ˈlavɾə̆ʑ ˈβaɕtə̃w], Brazilian Portuguese: [ɐw ˈbõ̞(w̃) ĩtẽ̞de̞ˈdox ˈpo(w)kə̻̆s pɐˈlavɾə̆z ˈbaɕtə̃w])
—roughly equivalent to the English proverb “A word to the wise is sufficient,” or, a more literal translation, “To a good listener, a few words are enough.”
There are also some significant differences between Brazilian Portuguese and European Portuguese as there are between British and American English or Peninsular and Latin American Spanish. This article notes these differences below only where:
both Brazilian and European Portuguese differ not only from each other, but from Spanish as well;
both Peninsular (i.e. European) and Latin American Spanish differ not only from each other, but also from Portuguese; or
either Brazilian or European Portuguese differs from Spanish with syntax not possible in Spanish (while the other dialect does not)._